MINNESOTA'S MINERAL HERITAGE

CONSERVATION BULLETIN NUMBER TWELVE MINNESOTA OF CONSERVATION

This document is made available electronically by the Minnesota Legislative Reference Library as part of an ongoing digital archiving project. http://www.leg.state.mn.us/lrl/lrl.asp (Funding for document digitization was provided, in part, by a grant from the Minnesota Historical & Cultural Heritage Program.) Author's Foreword Our natural resources constitute the foundations· of our well-being. the means of our protection, the hope of our future. The resources of any region determine to a marked degree .the activity of its inhabitants. Minnesota, though known as an agricultural state, has great mineral wealth and many of its citizens are engaged in mineral industries. Only ten states exceed Minnesota in the value of their annual mineral output. Of these ten, six are the great oil-producing states, three are the coal-producting states of Pennsylvania, West Virginia and Illinois, and one is California with its oil and gold. All of the mineral substances produced from the rocks of the states may be considered industrial minerals. Some are metals and others are non-metals. Metal mining· is restricted to the iron ranges, but the non-metals include a great variety of materials, such as limestone, agricultural lime, dolomite, marl, sand and gravel, clays and shales, wool rock, structural and architectural stone, etc., which are excavated and processed at many different places in the state. In the preparation of the articles in this bulletin, the main objective of the author was to acquaint the citizens of the state with the nature and extent of our mineral heritage. It is hoped that the publication will be instrumental in arousing greater interest in the many undevel­ oped mineral resources of our state. In assembling the data in the individual articles, many of the reports and bulletins issued by the Minnesota Geological Survey were used. The author gratefully acknowledges and gladly expresses his obligation to the members of that Survey who made the original investigations. For greater details the reader is referred to the original reports listed in the appendix to this bulletin. G.A.T. CONSERVATION BULLETIN NUMBER TWELVE

MINNESOTA'S MINE AL HERITAGE By GEORGE A. THIEL Professor, Geology and Mineralogy Chairman, Department of Geology and Mineralogy University of Minnesota

MINNESOTA DEPARTMENT OF CONSERVATION Saint Paul, Minnesota 1947 Our stone industry is more than a century old.

Stone for Sturdy Structures

Over 50 Kinds Are Quarried in Minnesota George A. Thiel Minnesota has natural mineral re- cultures on the basis of the use of sources of great abundance and wide stone and many of the ancient cul­ diversity of character and of location. tural groups produced work that still These have played a major part in holds the admiration of modern art­ the development of our Common- ists. The history of the civilizations of wealth, as they account for a high the past is recorded in their stone percentage of the state's in- .------buildings. Time has mellow- dustry. The last 50 years Minnesota's ed the color of the rock have been characterized by Mineral minerals, but the rock is still an enormous increase in the Heritage intact. utilization of a 11 mineral • • • The stone industry in Min- products. In fact, during this !Vu~ C11e nesota began more than a period more mineral wealth century ago when limestone has been extracted from the earth was quarried to build part of Fort than during all its previous history. Snelling. From this small beginning It is apparent that such an accele- in the early history of the territory, ration of production must be accom- the industry has progressed, with pe­ panied by the adaptation of conserva- riods of fluctuation and retardation, tion practices; for, if our present until today it has become the second economic and social system is to be in value in the mineral production maintained, it follows that a steady of the state. The stone industry now How of mineral products must go to gives employment to hundreds of per­ our industries. sons, from trained administrators and BUILDING STONES salesmen to quarrymen and skilled Ever since man has dwelt upon the stonecutters and carvers. During the earth's surface, stone has been used past ten years many new varieties of in the construction of his dwellings. stone have been located and quarried Even the cavemen had subterranean for commercial purposes and great homes of stone that Nature designed strides have been made in the meth­ and sculptured out of solid rock. The ods of quarrying and fabricating anthropologists classify early human stone. Modern machinery has elimi- 4 STONE FOR STURDY STRUCTURES 5 nated much of the tedious manual · mineral matter. When this process labor, and wastage has been greatly takes place in large masses far below reduced by the utilization of various the surface of the earth, the masses by-products. Today more than fifty are called batholiths. Some batho­ distinct varieties of architectural liths are scores or even hundreds of stone are quarried and fabricated in miles across, extending downward to this state. For many years Minnesota great but unknown depths. Because stones enjoyed a national reputation of their great size they cool and for beauty and adaptability before crystallize slowly and are therefore their merits were recognized by our relatively coarse-grained like the com­ local builders. The inadequate con­ mon granites. The natural processes ception that most people have of the of disintegration and transportation, importance of the stone industry in acting through geologic ages, have Minnesota was evident to the writer carried away the rock formations that from the surprise shown by many per­ were formerly over the batholiths and sons the first time they saw polished today our granite quarries, such as samples of the many beautiful varie­ those in the St. Cloud region, are in ties of granites, limestones, dolomites, the exposed granite masses. and sandstones that are taken from local quarries. Some molten matter may reach the surface and flow out as lava. When The essential qualities of building lavas are exposed to the air they cool stones are strength, durability, work­ rapidly and are so fine-grained that ability, color, and beauty. The prop­ the minerals in them cannot be recog­ erties required for diHerent uses vary nized. A dark-colored lava rock, com­ greatly, depending upon the type of monly called traprock, is very abund­ structure for which the stone is to be ant at Taylors Falls and along the employed. For bridge spans great north shore of Lake Superior. It is strength is essential; for monuments quarried and crushed for use as con­ and other outdoor structures, appear­ crete aggregate, road material, and so ance and resistance to weathering are forth. required; and for interior decoration, pleasing color and adaptability to The granites that are being utilized carving, and polishing are the most commercially are found in three wide­ important properties. ly separated regions in Minnesota: The three main classes of rocks ( I ) central Minnesota, particularly in from which our stone products are the region of the city of St. Cloud; derived are igneous, sedimentary and ( 2) the upper Minnesota river valley metamorphic. IGNEOUS ROCKS are from New Ulm to Ortonville; and (3) formed by the solidification of molten the Arrowhead region, which includes 6 MINNESOTA DEPARTMENT OF CONSERVATION

the area north of Duluth in Sf. Louis, Most of the granites in the Minne­ Cook and Lake counties. sota valley are characterized by at­ The stone of the St. Cloud region tractive color tones in peculiar wavy may be grouped into three major veins and swirling figures. Because of types, namely, pink granite, red gran­ these textural patterns, the granite ite, and gray granite. The difference has been given a variety of trade in color is due mainly to the character names, such as Rainbow, Tapestry, of the feldspar minerals in the rock. Oriental, Variegated, etc. Its varia­ These may be colorless, pink, deep tions in color and texture make it es­ red or gray. The pink granites are pecially desirable for facings, col­ quarried southwest of St. Cloud. They umns, and certain types of interior are best described as a stone with work. Huge polished slabs may be large pink crystals set in a finer­ seen as facing on many large office grained black and white matrix. The buildings, such as the Telephone finished stone is marketed under such Building and the Baker Building in trade names as Rockville Pink, Cold Minneapolis, the Daily News Build­ Spring Pearl Pink, Original Minnesota ing in Chicago, the City Service Pink, and Sauk Rapids Pink granites. Building in New York City, the San The red granites owe their color to Juanto Building in Houston, Texas, llie orthoclase feldspar which is deep and many other equally prominent red and ·constitutes about 75 per cent structures. of the rock. The granite is marketed Black and green rocks that are under a variety of trade names, such petrographically known as gabbros as Indian Red, Rose Red, Melrose and diorites are quarried in the Ar­ Red, Ruby Red, Mahogany Red, etc. rowhead region and sold under such Much of the rock is used for monu­ trade names as Emerald Tone, and mental purposes, but some archi­ Arrowhead Black Granite. tectural stone is also fabricated. SEDIMENTARY ROCKS repre­ The gray granites owe their color sent the accumulated sediments car­ to gray feldspars and associated black ried by the rivers to basins of sedi­ minerals such as hornblende and mentation where the river waters mica. Various shades of gray occur, come to rest. In this way vast layers depending upon the ratio of feldspars of sediment accumulated on the to black minerals. The gray granites floors of primordial seas. Slowly the south of Mille Lacs Lake, in the re­ loose debris was cemented together gion of Isle and Warmen Creek are with lime, silica and other minerals rather light gray due to the presence which were carried in solution by the of nearly colorless feldspars with water that filtered through it. The black hornblende. early sediments were buried deeper STONE FOR STURDY STRUCTURES 7 and deeper by succeeding deposits, limestone that varies both in color until eventually they were compact­ and in texture. Several ledges or ed and cemented in layers of solid strata of different color are found in rock. All sandstones, limestones, dolo­ the Mankato-Kasota district, and mites, and shales have been formed when used at random, these blend by such processes. Today such rocks beautifully and give individuality to are exposed at the surface where they the structures. Most of the stone is a are quarried and used extensively as fine-grained dolomitic limestone, yel­ structural and architectural stone. low and yellowish pink in color. Cer­ The numerous marine fossils in the tain ledges of the yellowish stone strata give evidence of their origin on have solution cavities that give it a the floor of the sea. texture similar to that of travertine. In some localities, limestone quar­ When sawed across the bedding ries were opened to obtain stone for planes, it is called Veine and when certain specific structures, on the com­ cut parallel to the beds its design is pletion of which the quarries were called Fleuri. The yellow stone is abandoned. Along the Mississippi used for decorative details because of River Valley rip-rap is quarried ex­ its rich color, with markings a trifle tensively for engineering projects in darker in shade.· Such shadings are the valley, and in the driftless and also characteristic of some of the pink loess-covered areas, where gravel is varieties. The selection of Minnesota scarce, much limestone is quarried dolomite for the exterior of the Art and crushed for highway construction Museum Building in Philadelphia work. In several localities, limestone demonstrates the widespread appre­ is burned for the manufacture of lime, ciation of our architectural stones for and some dolomite is quarried for exceptionally fine buildings. cement. Prior to the war there was a steady demand for Minnesota limestone for (EmToR's NOTE: Those interested architectural purposes, and with the in further reading on this subject are growing desire for attractive, perma­ referred to The Architectural, Struc­ nent and dignified stone buildings, the tural, and Monumental Stones of limestone and marble industry should Minnesota by George A. Thiel and flourish again after the war. Archi­ Carl E. Dutton. It is Bulletin 25 of tects are becoming more and more the Minnesota Geological Survey and interested in variegated wall surfaces, was published by the University of and are building up a demand for Minnesota Press in 1935.) Each year 26,600 cubic miles of water fall on the earth's surface. Is There rWatei; Watei; Everywhere?

The Hydrologic Cycle - An Eternal Merry-g0-round George A. Thiel Life would be scarcely worth B. Water vapor condenses to form living,-if, indeed, it could be rain or snow, which falls to the sur­ i maintained,- without an ade­ face of the earth but then evaporates quate supply of pure water. That is before infiltration takes place. Thus the reason villages and cities have the water returns to the atmosphere spent uncounted billions of dollars, in before becomiNg underground water. the aggregate, to establish C. Water vapor condenses the water supply systems Minnesota's and falls to the ground as which yield safe and pure Mineral rain or snow. The water water every time you open Heritage seeps below the surface a faucet in your home. This where (I) it may be held water may have been deep temporarily as soil moisture within the earth, in lakes or ·------JI and then be returned by streams many miles away. But, you plant transpiration and evaporation, may ask, where does it all come from? or ( 2) may percolate downward to­ The answer to the above question ward the zone of saturation. is really very simple. Nature actually Some of the water from the rain practices conservation. She uses the or snow that percolates beneath the same water over and over again, even surface is stored only temporarily as though the forms in which it occurs perched ground water, or flows may vary exceedingly. Most of the through the pores of the loose mantle water we use today has been circu­ rock quickly enough to augment lating since the world began. This floods or to maintain high-water eternal merry-go-round is called the stages of the streams immediately hydrologic cycle. The processes in­ after the floods. Much of the water, volved may be summarized as fol­ however, sinks to the main water lows: table as free:..moving water and is A. Water vapor condenses to form discharged as effiuent seepage and rain, snow, or fog, which may evapo­ spring flow. This flow furnishes the rate again before reaching the earth's water of the streams during dry or surface. frozen seasons. A smaller percentage 8 IS THERE 'WATER, WATER, EVERYWHERE'? 9

Ra/n, Jnow, !toil, etc.

z 0 ~ a 0 Q. &oport1fion while follinJ or from surfaces <( >w

T1Y1nspir1Jtion from soil throu/h f'lonb

THE HYDROLOGIC CYCLE. It has been estimated that a drop of water evaporated from the ocean rains five times before it gets back to the sea. (After National Resources Board Report.) may move as confined water in and INFILTRATION OF GROUND WATER through ground-water conduits. It Infiltration is the movement of may percolate through such artesian water from the surface of the earth aquifers for hundreds or thousands of into the soil and rocks of the earth's years before it is returned to the sur­ crust. The amount of meteoric water face or discharged on the floor of the that penetrates the earth is determin­ sea.. Some water apparently remains ed by several factors, chief of which entrapped in deep-seated rock for­ are ( 1) the amount and kind of pre­ mations for large units of geologic cipitation, ( 2) the rate of precipita­ time. tion, ( 3) the slope of surface, ( 4) 10 MINNESOTA DEPARTMENT OF CONSERVATION the porosity of soil and rock, ( 5) the surface. Forests and meadows hold structure of the rock formation, ( 6) back the run-off and also retard evap­ the amount and kind of vegetation on oration. If the humidity is low imme­ the surface, and ( 7) the amount of diately after a shower, much of the moisture in the atmosphere. Within rain evaporates before it can sink in­ certain limitations the amount of wa­ to the earth. This is especially true ter that soaks into the ground is de­ in arid regions, where even after termined by the amount of precipi­ heavy rains most of the water evapo­ tation as rain. In desert areas, ground rates and passes again into the at­ water generally lies deep, and little mosphere. water occurs near the surface. The For a given drainage basin the ap­ more rapid the rainfall, the less the proximate rate of infiltration can be amount of water that sinks into the determined if stream-gauging stations earth, for the surface soon becomes have been installed, and if there are saturated. The same is true of the adequate records of both the amount melting snow. The more rapid the and the intensity of rainfall on the rate of melting, the less the amount of various geographic units of the basin. water that sinks into the ground, es­ The type of land usage in each unit pecially into frozen ground. The of the drainage basin must also be steeper the slope of the ground, the considered. Virgin soil possesses the greater the percentage of the run-off. structural characteristics that are most The flatter the ground, the greater favorable in promoting infiltration. the amount of water that will sink Native grasslands, forests, and areas below the surface, because the run­ of rotated crop land allow a more off is retarded, and the water has a rapid infiltration than intensively cul­ longer time to soak into the ground. tivated lands that are low in organic Weathered and stratified rocks are content. It has been shown that cul­ more favorable for the entrance of tivation destroys natural structural water than most igneous rocks. In­ aggregates and thus causes soil par­ clined strata will allow more water ticles to gradually assume a position to penetrate than flat-lying beds. Wa­ of closer packing. ter passing down inclined beds will WHAT DETERMINES THE YmLD OF follow the most porous layers. If GROUND WATER the rocks are horizontal, the water If a high percentage of the rain passing downward must cross also the that falls on the earth percolates in­ less porous beds. Plants and organic to the rocks, there should be "water, material derived from plants check water, everywhere," below the sur­ the flow of surface water, causing face. If so, why isn't it possible to the flow of water to sink below the dig or drill a well anywhere in Min- IS THERE 'WATER, WATER, EVERYWHERE'? 11 nesota and obtain an ample supply of From St. Cloud northward to the Ca­ water? The answer to this question nadian boundary and westward to the is found in the variation in the po­ Red River valley, the glacial drift rests rosity and permeability of different on very ancient crystalline rocks that kinds of rocks and subsoils. Some have a porosity of less than 2 percent. rocks are very permeable. That is, Over that entire area, the only re­ the pore spaces are sufficiently large liable source of ground water is the that water can flow through them unconsolidated glacial drift. In many freely. communities these glacial deposits are Well-sorted deposits of uncement­ composed of unsorted boulder clays ed gravel, sand, or silt have a high that are quite impervious, and even if porosity, regardless of whether they they are saturated with water, the consist of small or large grades. How­ flow is so slow that the yield of a well ever, if the material is poorly sorted, is small. In areas where layers of sand small particles occupy the spaces be­ and gravel are interbedde·d with the tween the larger ones, still smaller clay, ample supplies of water are pro­ ones occupy the spaces between these duced from the coarser sand and small particles, and so on, with the gravel strata. result that porosity is greatly reduced. Most of the southwestern part of Boulder clay, which is an unsorted the state, from Swift and Kandiyohi mixture of glacial drift contain:iing counties southward to the Iowa-Min­ particles of a great variety of mate­ nesota line, is underlaid by a series of rials of varying sizes, may have a very marine sandstones and shales that oc­ low porosity, whereas outwash gravel cur under the glacial drift, and they and sand derived from the same rest in turn on the granites and other source but sorted by running water crystalline rocks such as are exposed may be highly porous. Well-sorted in the Minnesota Valley near Granite and uncemented gravel may be com­ Falls, Morton, and Montevideo. posed of pebbles that are themselves These marine sandstones yield water porous, so that the deposit as a whole copiously but much of the water con­ has a very high porosity. Well-sorted tains such high percentages of dis­ porous gravel, sand, or silt may solved mineral salts that it is unfit for gradually have its interstices filled domestic and industrial use. Here with mineral matter deposited out of again, the purest water occurs in the solution from percolating water. glacial drift. From the standpoint of the yield The southeastern counties, from of ground water, Minnesota may be Wright county southward to Man­ divided into three major areas, each kato, and eastward to the Mississippi with its own water supply problems. River are over an area where the 12 MINNESOTA DEPARTMENT OF CONSERVATION

rocks below the glacial drift contain twelve thousand years. Nearly three­ layers of porous, marine sandstones fourths of this rainfall again vaporizes. such as those exposed in the walls of What remains flows back to the sea the valleys of the Mississippi and St. in rivers. An amount of water equiva­ Croix rivers. These sandstone strata lent to the whole volume of the ocean have a porosity of from 20 to 35 per­ has done this at least thirty thousand cent and, where saturated with times during the known duration of ground water, wells that penetrate geologic history. them yield from 500 to 1000 gallons per minute. Structurally, these rocks The total annual fall of meteoric form a broad, trough-like structure, water on the earth's land areas is one margin of which crops out along about 26,600 cubic miles. This pre­ the Mississippi Valley, and the other cipitation varies greatly both with re­ occurs under the glacial drift in the spect to geographic location and time. counties to the north and south of Furthermore, it may be in the form Mankato. The Twin Cities area is a of rain or snow. In polar regions the local, saucer-shaped basin at the snowfall represents from eight to fif­ north end of the larger trough-like teen inches of water, whereas, oncer­ structure. Because of these struc­ tain slopes of the Himalayas, the rain­ tural relations, southeastern Minne­ fall may be. as much as five hundred sota is endowed with an exceptionally inches a year. In dry regions, such large supply of artesian water. as the vast desert areas of northern In order to more fully appreciate Africa, central Asia, Australia, and the variation in the distribution of along the coast of Peru, only a few water in the land areas of the earth, inches of water are precipitated annu­ a few words regarding the role of ally. Among the Canary Islands, sur­ the atmosphere in transporting water rounded by water, are localities that from the ocean to the land may not have very little rainfall for periods as be amiss. long as three years in duration. Such The earth's atmosphere constitutes great variations in rainfall raise im­ slightly less than a millionth part of portant problems in agriculture, for­ the earth's whole mass. But the rain estry, and water supply engineering. which falls from the atmosphere ev­ But regardless of where the raindrops ery century weighs seven times as may fall, they inevitably return to the much as the air itself. Three-fourths clouds to start the cycle all over of this rain falls back into the ocean. again, "to be renewed in eternal Even so, the work of the atmosphere resurrection," as Emil Ludwig thus amounts to pouring all the water of beautifully describes the hydrologic the oceans over the land once in cycle in his book on the Nile. IS THERE 'WATER, WATER, EVERYWHERE'? 13

~PALEOZOIC ~CRETACEOUS

~ PRE-CAMBRIAN

GENERALIZED MAP OF MINNESOTA, showing the major areas of pre-Cambrian, Paleozoic, and Cretaceous rocks. Each area is a separate ground-water province. In the pre­ Cambrian area water must be obtained from the glacial drift. The Paleozoic rocks are in­ clined and contain porous aquifers. The Cretaceous rocks are mainly horizontal shale beds, with some sandstone members. (This map and the sketch on page 11 are reproduced from the Geology and Underground Waters of Southern Minnesota by George A. Thiel, through courtesy of the University of Minnesota Press.) Nearly every county of the state has some commercial clay.

The Potters Clay

One of Earth's Commonest Materials George A. Thiel Ordinary clayey soils are among Deposits of clay are of two general the commonest materials at the sur­ types, residual and transported; but face of the earth. There are two def­ in all cases the clay is of secondary initions of clay in common use; the origin, that is, it was formed by the first is that used by the ceramists or alteration of some other rock. The clay technologists, and the second is residual deposits were formed by the the geologists' definition. alterations or decomposition The ceramist defines a clay of a rock in place. This al­ Minnesota's as a natural-occurring min­ teration may be of two eral substance which is Mineral types, one involving chemi­ more or less plastic when Heritage cal change resulting in the wet, and which when heat- ;1;umk/j, 7/uee formation of clay, the other ed to redness or above, be- involving simple solution comes permanently hard. The geol­ of a rock containing clayey im­ ogist, on the other hand, defines clay purities and the consequent deposi­ as a mixture of minerals composed tion of the insoluble clay. Residual essentially of hydrous aluminum sili­ deposits of the first type are usually cates (predominantly K a o 1 n i t e, formed by the chemical alteration of

H 4A12Si2 0 9 in particles which range granites and other rocks which con- in size from approximately 0.005 mill­ -tain a high percentage of feldspar. imeters to submicroscopic. The alteration of pure feldspars re­ Clays are seldom pure. They com­ sult in pure kaolins, whereas the al­ monly contain various amounts of teration of granites results in mix­ such minerals as quartz, calcite and tures of kaolin, silica and mica, to­ feldspars in a fine state of division gether with other impurities origin­ or as grains the size of silt and sand. ally in the granite. Thick deposits of Mort clay is so soft that you can dig such white kaolintic mixtures may be it with a spade or cut it with a knife. seen in the roadcuts in the region of Its colors range from white to green, Morton, Redwood Falls and Ft. brown or brick-red. Hard and indur­ Ridgely. In humid tropical or sub­ ated clays are called shale. tropical regions the residual clays are

14 THE POTTER'S CLAY 15 red, brown or yellow because the ever, it should be noted that no class­ iron compounds in them are oxidized ification is perfect, for one clay may and often combined with water to be adapted to several widely differ­ form the red and yellow oxides of ing uses. iron such as hematite and limonite. High-grade clays include white­ Deposits of sedimentary or trans­ ware clays, pottery clays, refractory ported clay5 may have settled on the clays and medicinal clays. The flood plains of valleys when shallow whiteware clays may be plastic or rivers overflowed. Other were trans­ nonplastic and they are composed ported and settled to the floors of chiefly of white kaolin. They are lakes and swamps that are now used in the manufacture of porcelain, drained and still other deposits settl­ china, pottery and high-grade tile. ed to the floor of the inland seas that Non-ceramic uses include such things occupied this area at intervals dur­ as "filler" for paper, cloth and win­ ing the distant geologic past. Such dow shades, as coating for wallpaper marine clays and shales contain many and in the manufacture of rubber, petrified corals, bryozoa and other oilcloth, soaps and toilet and tooth sea-dwelling animals. Marine fossils powders. It is used also as an invert are abundantly present in the shale extender of paints and white washes pit of the Twin City Brick Company and as an adulterant in candy, food plant in St. Paul. products, medicinal powders and Many of the transported clay de­ other products. posits in Minnesota are of glacial or­ Refractory or fire clays are clays igin and were deposited as glacial which endure high temperatures lake clays, river clays or till plain without change other than dehydra­ clays. tion. Their principal uses are in mak­ CLASSIFICATION OF CLAYS ing fire brick and other heat resisting BY USES materials required in the iron and Clays have been classified upon steel industry and in making coke. many different bases and in many Refractory clays must be relatively different ways. Thus, they may be free from minerals that act as fluxes, classified according to their mode such as calcite, dolomite, iron car­ of origin as outlined above, or ac­ bonate, and excessive silica. Flint cording to their chemical or physical clay is a non-plastic, hard, dense re­ properties, their uses, or combina­ fractory clay, having an appearance tions of any or all of these methods. much like flint. From a commercial standpoint, prob­ Pottery clay is a general term that ably the classification by properties includes some refractory and some and uses is most important. How- vitrifying clays. They have high plas- 16 MINNESOTA DEPARTMENT OF CONSERVATION

96 92 90

0

COMMERCIAL CLAY DEPOSITS IN MINNESOTA Lege/7d: / 8order OT Lo/r-e Agoss/z ..Oepo.s/TS. -46 ~ Areo OT Oecoroh Sho/e~ /Veor SurT'ace. A Opero//:Og /940( Pd's //7 !::. Ooce /.1-1:vA-ed./ LJecoroh. • operor/ag /940( P/r..s //7 O 0/7ce 11/or/r-ed../Arc/Jeon_, A'es/duo/$C.,·-eT. C/oys. Ill Ope/OT//7§ /940( P/r.s //7 o Ooce J-YorA-ec(/ Red-i'>vo?­ /ag G/oc/o/ C/oys. + Ope/aT/O§ /94q) P/T.5 //? .: ... · OOace nvr/r-ed/Creo/77- : ..O'. ·: ovro/ag G/oc/o/ C/oys. · x P/r.s /O Rece/7r f---'-i~WJ<~==¥~~o· .. · . . R/ve.r,i! LoA-e C/oy.s . ....,\ _ · X (.)Areo CovererZ- 4 -114- ·.·\'.., 4 .. D .. <> ~-":"'---L..._:.-0.1 _ 0_L__--1. _ _'.:__J_____!;:!._J___ .L.Ji~ZLL- -6:l'.-'w .....="°.:....:.-. ~·:...:JU'iTh Loess I I

I 91$ 9.¢ 921 ..?O THE POTTER'S CLAY 17 ticity, great tensile strength, and colorizing and stabilizing petroleum complete retention of form while be­ lubricants. The remaining 10 per ing burned. They are, as a rule, semi­ cent is used chiefly. in the fat and refractory and burn to a dense, rigid vegetable-oil industry. mass. The common products mami­ The decolorizing action of adsorb­ factured from such clays are earthen ent clays on oils is not a filtering or and stoneware-both plain and dec­ straining action, but a selective ad­ orated, crockery and glazed ware, sorption, such as occurs in dyeing various color combinations may be fabrics. The dye leaves the solution produced by changing the content of and adheres to the textile fibers and iron and maganese. will not wash off. In a similar man­ Low-grade clays. As the name im­ ner, the darker constituents of oil are plies, these clays are composed of adsorbed on the clay, leaving be­ less well-sorted materials and many hind the colorless constituents. The are of the vitrifying type. That is, result is a clear, nearly colorless veg­ they fuse to a glassy vitreous mass etable or mineral oil. or take on a glassy glaze when burn­ Adsorbent clays are used too for ed. Many low-grade clays contain renovating dry-cleaning fluids such as considerable iron which acts as a flux naphtha, gasoline and chlorinated and gives color to the glaze. The hydrocarbons. If the proper amount good clays of this type have a wide of clay is added to a batch of clothes range in temperature between incipi­ being cleaned, the cleaning fluid re­ ent and complete fusion. They are mains water-white at all times and used to make terra-cotta ware, roof­ acts merely as a solvent and carrier ing tile, hollow drain tile and glazed between fabric and clay. water pipes, and paving bricks. Al­ MINNESOTA'S COMMERCIAL CLAYS most any kind of clay which possess­ Clays in Minnesota were used for es plasticity can be used for common the manufacture of brick as early as brick. Red-burning clays are pre­ 1862, and by 1884 it was being used ferred as they harden at a low tem­ to make pottery, drain tile and fire perature. brick. Nearly every county in the Adsorbent clays. The use of cer­ state has some clay that may be used tain clays as bleaching or decoloriz­ commercially. Clays of marine origin ing agents was known to the anci­ occur in two geologic formations­ ents. The Chinese have used "soap" the Decorah shale of Ordovician clays in removing oil and grease age and the Benton shale of Creta­ from wool and textiles for thousands ceous age. The Decorah shale ex­ of years. Today about 90 per cent tends from the Twin Cities south of the adsorbent clay is used for de- and southeast and the Benton shales 18 ~MINNESOTA DEPARTMENT OF CONSERVATION

are found at widely scattered points produced many tons of high-grade from Brown county to Goodhue brick and tile clay. county. It is being used on a large Wind - deposited material known scale at Springfield in Brown county. as loess, and composed of fine silt The residual clays in Minnesota and clay, mantles most of the sur­ have resulted from the weathering face in an area in the southeastern of pre-Cambrian granites. They oc­ part of the state embracing much of cur beneath the glacial drift over Goodhue, Olmsted, Wabasha, Win­ large areas in southwestern and west­ ona, Fillmore and Houston counties, central Minnesota. They crop out and parts of Mower, Dodge, Rice along the Minnesota valley in Ram­ and Dakota counties. On the upland sey State Park north of Redwood plateaus of these counties it attains Falls and near Richmond in Stearns a thickness of 25 feet. This loess was county. Well records indicate that, deposited originally as fine glacial at many places, white kaolinitic clays outwash, but later it was transported attain a thickness of 50 to 100 feet. by the wind and redistributed over Glacial lake clays occur in the area the surface of the drift. The more southwest of Duluth, in what was the clayey varieties of the loess can be bed of glacial Lake Duluth. There used in the manufacture of brick. are large deposits of red plastic clay The city of Red Wing has long that were reassorted by stream and been famous for its .ceramic indus­ wave action and are now excellent tries. At the present time they utilize brick and pottery clay. It has been about 50,000 tons of clay annually. mined extensively in the region of They now manufacture much orna­ Wrenshall. mental pottery, including such ar­ River valley clays occur along the ticles as jars, jugs, flowerpots, mixing wide valleys of the Mississippi and bowls, casseroles and other house­ Minnesota rivers and their major hold accessories. tributaries. These are banded, gray, Minnesota's clay resources have glacial clays laid down thousands of been prospected by the Minnesota years ago when these streams car­ Geological Survey in sufficient de­ ried sediment-laden water from the tail to assure a supply for many de­ melting ice sheet. Clays of this origin cades. Geological indications in the have been used at Chaska and Jor­ areas now being mined are most en­ dan along the Mississippi river from couraging, and it is very likely that Minneapolis to Brainerd. The old pits future prospecting will disclose ad­ at Coon Creek, north of Minneapolis, ditional reserves. Iron occurs in nearly all classes of rocks and mineral deposits. Iron Ores-Our Minerals of Might

They Fired the Arsenal of Democracy George- A. Thiel Iron is the fourth most abundant the formation of sedimentary iron de­ element in the earth's crust, and it posits have occurred at many times is nature's most common pigment. in the remote past. These conditions The red, pink, orange, brown and were often very similar in widely green colors in rocks and soils are separated areas. So similar are the caused mainly by iron compounds. pre-Cambrian iron formations of Comparatively small amounts ~------Minnesota, Wyoming, Lab- o£ these compounds produce Minnesota's rador, Brazil and India that conspicuous colors. The bril- Mineral geologists are scarcely able liantly colored sandstones of Heritage to find diagnostic mineralo- the Painted Desert, or the • • • gic differences. "Red-beds" of the Spearfish !Vumk4 qcm/l, The iron formations on region of South Dakota, the three ranges in Minne­ contain no more than 5 to 10 per sota (see map) slope or dig toward cent of iron. the basin of Lake Superior, and those Iron occurs in nearly all classes of of northern Michigan and Wisconsin rocks and mineral deposits, but its dip north or northwest. Most of the ores are concentrated in small and central part of the Superior basin widely scattered areas. By far the is occupied by basic lava flows, com­ most important single class is sedi­ monly called trap-rack, and by the mentary iron ore but many large great intrusive masses of "black gran­ deposits belong to the groups known ite" or gabbro that may be seen in as magmatic segregation and con­ the hill at Duluth. The character of tact metamorphic ores. Of the many the sedimentary rocks and the suc­ iron minerals known, only the oxides, cession of the different lithologic types are very similar on the two hematite (Fe203 ), magnetite (Fe30 4 ), and limonite (a mixture of hydrated sides of the Lake Superior basin. iron oxides), the carbonate siderite The accompanying map shows the (Fe C03 ), and the ferrous silicate geographic location of the iron-bear­ chamosite are important in ores. ing rock formations and of the more Geological condition~ favorable to important magnqtic lines ill Minne-

19 20 MINNESOTA DEPARTMENT OF CONSERVATION

sota. These rocks were originally that are several miles long, 1,000 feet formed from gelatinous accumula­ wide and from 200 to 400 feet in tions of marine precipitates of silica depth; the trough-like shape of the (Si02 ) and iron compounds. This ore body is due to the natural slump material later hardened into dark­ that takes place in the ore as the gray bedded strata that became as silica is removed from the taconite. hard as flint and contained no more An original thickness of 100 feet of than 20 to 30 per cent of iron. Where taconite forms about 65 feet of con­ these rocks are still unaltered they centrated ore. Fissure ore bodies are called taconite or ferruginous are much smaller than troughs and chert. The banded jaspery chert of may be only 2 or 3 feet wide, with the Soudan iron formation on the a depth of as much as 100 feet and Vermilion range is called jaspilite. a length that may be 200 feet. Flat­ Where much of the iron has been lying ore bodies may look like troughs oxidized they are known as oxidized whose upper portions have been erod­ taconite, and where a high percent­ ed, or they may be layers of ore which age of the iron has been recrystalized follow some particular flat-lying hor­ to magnetic iron, they are called izon of the iron-bearing formation. magnetite taconite or magnetic ta­ The Soudan iron-formation of the conites. Only in restricted zones Vermilion range (see map) is not where the silica has been leached a single large extensive iron-bearing out by waters circulating through bed like that of the Mesabi Range, .cracks and fissures has the taconite but consists of lenses of relatively been converted into commercial ore. small dimensions. These were folded If the Biwabik iron formation. were very complexly during the mountain­ exposed to view by removal of the building epochs that preceded the glacial drift and the cretaceous sedi­ deposition of the Biwabik iron form­ ments (See figure 2) from the region ation. The conspicuously banded of Grand Rapids to Babbit, not more character of the Soudan formation than 10 per cent of the area of the makes it easy to observe the folding, formation would be found to contain which, in most localities of outcrop, enriched ore. The remaining 90 per is very intense. The ore bodies at cent or more would be some form Tower and Ely are as irregular in of taconite. outline as the formation itself. The Most of the ore bodies on the ores are mostly hard and dense blu­ Mesabi Range have one of three ish, crystalline hematite that is an shapes-trough, fissure, or flat lying. exceptionally fine material for the The trough-shaped deposits range in blast furnace. size from widened fissures to some On the Cuyuna Range the iron- IRON ORES-OUR MINERALS OF MIGHT 21

92 91 90·

- /Jeronion limestone § Ordovicion ~~7.~t°/:'· DCambrian ~:z";,~f,;~· · G Cambrian? f~r~~J'·x 0 lr'eweenawan ~~~1r~ ~ /(eweenawon //,~:'c,~;t",$ QJ V't,':,~~~';/'ot~ion f;:::,of,on [bill L ovrenhoa qrofJ!le

qreen·

~ILtS

94 92·

Fig. 1. (map) Geologic map showing locations of iron-bearing formations. (From Mineral Resources of Minnesota, published by Univ. of Minnesota Press.) 22 MINNESOTA DEPARTMENT OF CONSERVATION bearing rocks in seven or eight main creased. The record shipment to belts, some being less than a mile date (from L. Superior dist.) was long, and others extending almost 91,542,000 long tons in 1942. In continuously for many miles. The 1944, 79,868,000 tons proved ade­ most productive part of the range quate to supply the war industries. is in Crow Wing county. Here the When we realize that in 1940, 14 ore bodies are roughly tabular in of our mines each produced over a shape, the longer axes being parallel million tons of ore and more than· a to the bedding of the enclosing rocks. · half million tons were taken from Their widths range up to several hun­ each of 28 mines, it may well cause dred feet and their lengths to poss­ us to wonder how long our supplies ibly a mile. Some are shallow; others will last. are as much as 700 feet deep. There are a number of ways in The average iron content of Mes­ which conservation may be accomp­ abi Range taconite is given in the ac­ lished and some of these are already companying table which represents being used. Taconite or low grade a compilation made by E. W. Davis, ore, which owes its low iron content Director of the Mines Experiment to the presence of a high percentage Station at the University of Minne­ of silica ( Si02 ), can be enriched or sota. concentrated by one of several pro­ During the pre-war period, 1926- cesses. An interesting example is the 1940, the world produced annually type of taconite that contains mag­ an average of 145,000,000 tons of netic iron oxide. This oxide is at­ iron ore, 80,000,000 tons of pig iron tracted by a magnet. Thus, if the and 101,000,000 tons of steel. Dur­ lean ore is crushed so as to separate ing that period the Lake Superior dis­ the mineral grains, it is possible to trict normally produced from 3,000,- pass the finely divided mineral grains 000 to 60,000,000 tons annually. over magnets which remove the iron­ About two-thirds of this tonnage bearing grains from the valueless came from the Mesabi Range. Dur­ minerals. The result is that a mag­ ing the war, however, the amount netic taconite which did not con­ mined and shipped was greatly in- tain more than about 20 per cent of

AVERAGE IRON CONTENT OF MESABI RANGE TACONITE %Fe % Fe %Fe % Fe as as as other Location Total Magnetite Hematite minerals East of Mesaba ------29.93 20.61 1.30 8.02 Mesaba to Nashwauk ------28.14 13.94 7.41 6.79 Nashwauk to Coleraine ------31.26 3.62 26.19 1.45 Rough weighted average ------29.12 13.23 9.94 5.95 IRON ORES-OUR MINERALS OF MIGHT 23

Fig. 2. Generalized geologic cross section of northern Minnesota in the vi­ cinity of the Mesabi range. All of the iron ore now worked on the Mesabi range is near the eroded surface of the Biwabik iron-bearing formation, below the Creta­ ceous sediments and glacial drift. iron might yield a concentrate with beneficiate them, the problem of as much as 48 to 60 per cent of iron. where to get iron ore in the United Non-magnetic or oxidized taconite States would be solved for many has most of its iron in the form of years. However, there can be no cer­ the mineral hematite ( Fe20 3 ). From tainty as to the amounts available or the standpoint of concentration, this the length of time such reserves will low-grade ore has certain advantages suffice our industry. It is' a simple over magnetic taconite. The oxidized matter to determine the cubic con­ low-grade ore is easier to drill, blast tents of an ore body and to estimate and crush. It is also more readily by analyses the amount of iron avail­ available since it occurs in the walls able to the ton of ore. At present the and on the bottoms of many of the question to be answered is, can the mined-out open-pit mines. However, low-grade ore be worked profitably? it is at present more difficult to con­ That question has so many unknowns centrate than the magnetic types. The and variables that the answers can methods now being studied to con­ be little more than mere personal op­ centrate the oxidized taconite include inions even from those most capable magnetic roasting, gravity methods of judging. As profit is the only mo­ and floatation. tive, except with government sub­ The total tonnage of available low­ sidies, any change in one or more fac­ grade ores, both magnetic and oxi­ tors may make a given method of dized, is enormous, and if cheap and beneficiation of low-grade ores a fin­ practical methods can be found to ancial failure or an outstanding sue- 24 MINNESOTA DEPARTMENT OF CONSERVATION cess. Statistics based on calculations hitherto regarded as unprofitable. If that assume a uniformity of condi­ funds for continuous research are tions throughout the entire extent of made available, the advance in tech­ the iron formation on the Mesabi nical skill will undoubtedly keep Range may be most misleading and pace with other economic develop­ result in gross misinterpretations. ments. However, research has already done much in aiding conservation, All minerals are a "one-crop re­ and it may be taken for granted that source" and Minnesota is singularly only beginnings have been made. fortunate in having a bumper crop There have been great improvements of iron ores. However, we can ex­ in the concentration of ore, and new tend the utilization period of that mechanical improvements will make crop if we succeed in governing its possible the beneficiation of taconites rate of harvesting. Purest beds in Minnesota are near Rochester and LeRoy.

Limestones

Cemeteries of Ancient Seas George A. Thiel Extensive strata of limestones and shells which can be seen only by mi­ dolomites occur beneath the mantle croscopic examination. Most of these of the glacial drift in the southeastern are similar to the foraminifera dredg­ counties of Minnesota. The beds ed up from the sea floor where cal­ crop out along the bluffs of the Mis­ careous ooze is collecting at the sissippi river and its major tributaries present day. such as the Minnesota, St. The sediments that later Croix, Cannon, Root, and Minnesota's produce limestone usually Cedar rivers. Mineral accumulate beyond the zones The natural architecture Heritage of sand and mud that in of limestones can be studied most places border the lands. in the walls of the numerous Jlt~ t/}.w.e However, where the sea is quarries that have been ex- "------' uncontaminated by muddy cavated in that area. When one ex- sediment and especially where the amines the rock closely, it is evident sea-cliffs themselves happen to be that most limesfones are accumula- made of older limestones, limy sedi­ tions of calcareous ( CaC03 ) organic ments may form close to the land. remains-vast cemeteries in which the Beaches may locally be composed of teeming life of the ancient seas has sand grains made up not of quartz, been entombed. Some limestones are but of shell debris. Similarly, the packed with the remains of corals sands associated with coral reefs and and marine shells, and the bead-like atolls consist largely of coral frag­ relics of the stems of sea-lilies. Others ments, ground to their present small are crowded with the coiled shells of size by wave action. ammonites or with the blunt, pencil- Limestones, dolomites, and marls like remnants of belemnites; the fine- are used in the manufacture of ce­ grained and friable limestone known ment and of quicklime or lime, as it as chalk contains tiny, smooth white is commonly called. Chemically it is shells and fragments of sea urchins. calcium oxide ( CaO). The greatest Besides these visible fossils there are use for lime is in the chemical in­ innumerable little coiled or globular dustry which, in 1939, used 2.2 mil-

25 26 MINNESOTA DEPARTMENT OF CONSERVATION

lion tons for a multiplicity of purposes Fertilizers Railway ballast sueh as bleaching paper pulp, sugar Finishing lime Refining ef quick- refining, tanning, water purification, Fungicide silver Gas manufactnre Refractory lime glass making, calcium cai:,bide, petro­ Glass-making Rip-rap leum refining, and many others (see Glue Road metal list) . During the same year building Insecticides Rubber manufacture purposes used a million tons and re­ Insulating Sand-lime brick fractory linings used nearly an equal Lime burning Sanitation Lithographing Salt refining amount. Much of the refuse from Milk of lime Silica brick limestone quarries can be used for Mortar Soda-ash products crushed stone. Some idea of the Oil, fat, glycerine, Stock feed crushed limestone industry may be and soap Stucco gained from the fact that more than Oil refining Sugar manufacture 66 million short tons were used for Ore flotation Tanning Paints and varnishes Textiles that purpose in the United States in Paper-making Water softeaer 1940. Disinfectant Wood distillation COMMERCIAL USES OF LIME­ Drugs STONES AND MARLS The limestones of Minnesota were Commercial uses of naturally oc­ formed during the Paleozoic Era, and curring calcium carbonate and manu­ vary in age from the Cambrian to the factured products in the preparation Devonian. They are nearly all more of which limestones or marls are uti­ or less dolomitic. (Dolomite contains lized: both calcium and magnesium car­ Absorbent of gases Bone ash Acetate of lime Building stone bonate.) The oldest dolomitic lime­ Acid neutralizer in Calcimine stone is the St. Lawrence formation. various industries Calcium carbide This bed is exposed in the Minnesota Agricultural lime- Calcium cyanide valley west of Jordan and in Nicollet stone Calcium light pencils and Blue Earth counties, near the Ammonia Calcium nitrate Ammonium sulphate Carbon dioxide village of Judson. It crops out also Basic steel Ceramics along the St. Croix and down the Mis­ Blast furnace flm.:: Chicken grit sissippi river to the southern boun­ Bleaching powder Chloride of lime dary of the state. At Red Wing it is Clarifying grain Plaster quarried and used in the manufac­ (milling industry) Portland cement Coagulator Potassium and sodi- ture of rock wool. Concrete aggregate um dichromates The Oneota and Shakopee forma­ Dehydrating agent Pottery glazes tions, which are highly dolomitic Deodorizer Preservative Dyeing Purification of sew- limestone, form the base of the Ordo­ Electrolytic work age vician system of rocks in this area. LIMESTONES 27

They are highly dolomitic limestones eastward along the southern branches which have supplied both lime and of the Cannon river, the western and building stone to the trades for many southern branches of the Zumbro years. These beds, varying in thick­ river, the western branches of the ness from 125 to 350 feet, are ex­ Whitewater river, and the upper parts posed along the Minnesota river from of the various branches of the Root Garden City northward to Chaska river. It has been used extensively where they pass below river level. as a building stone and for crushed Along the St. Croix they appear in stone in the area of the Twin Cities northern Washington county and and in the regions referred to above. continue southward in the river bluffs The purest limestones in Minnesota to the Mississippi river in the vicinity occur in the Prosser beds of the Ga­ of Hastings where it occurs near river lena formation and in the so-called level. From there it rises to the top lithographic beds of the Cedar Valley of the bluffs at Red Wing and con­ limestone. The former are exposed tinues to form the hill caps along the along the valleys in the area south­ valley to the state line in Houston east of Rochester, and the latter oc­ county. curs under a thin drift mantle in the The Platteville formation is the vicinity of LeRoy near the southern limestone that crops out in the valley state line southeast of Austin. walls around the Twin Cities in Hen­ (For a tabulation of. the composition of nepin and Ramsey counties. It is ex­ Minnesota limestones, see C. R. Stauffer and G. A. Thiel, The Limestones and Marls of posed also along Straight river at Minnesota (Minnesota Geological Survey, Faribault and from thence north and Bulletin 23, 1933) pp. 72-74.) Each grain of sand could tell a long geological story. The Sands of Time

They're Put to Wark in Minnesota George A. Thiel The poet Wordsworth once said, consolidated aggregates of such grains "Wisdom is ofttimes nearer when we are called sand. stoop than when we soar." Such a Sands may be classified in many statement contains good geological different ways-by origin, chemical or advice and therefore let us stoop and mineralogical composition, geological take an excursion among the sand or geographical distribution, grain grains. Each grain of sand- ·------size uses, or combinations of and there are billions of them Minnesota's two or more of these meth- on even a small beach-could - Mineral ods. The principal types of tell a long geological story. Heritage deposits based on the man- Such a biographical tale ner of deposition are (I) would include the events IV~ $etJ.en river sands, ( 2) lake-bed leading up the formation of ______, sands, ( 3) beach sands, ( 4) the crystals and grains of minerals in glacial sands, and ( 5) eolian (wind the ingneous rocks long before the blown) sands. individual crystals became grains of All of the above types of sand de- · sand. posits are found in Minnesota. Fur- Most sands are composed mainly of thermore most of the sands are very grains or pieces of quartz (Si02 ) but complex mineralogically. The reason many contain varying amounts of such for this complexity is that most of the minerals as feldspar, hornbJende, mag- sands in the state are of glacial origin. netite, mica, garnet, tuurmaline, apa- In other words, great, slowly-moving tite, zircon, and other minerals. All of ice sheets crushed and ground mil­ these minerals were once constituents lions of granite and other types of of massive rock formation such as boulders to particles the size of sand granites,. diorites, and others, that grains. As the glaciers melted, the were subjected to decomposition and water derived from the ice tended to disintegration under the ever-active sort the sand from the coarser pebbles processes of weathering and erosion. of gravel size, and much of the fine These processes liberate and sort the clay was carried in suspension to more unaltered mineral grains and the un- distant basins of accumulation by the 28 THE SANDS OF TIME 29 glacial outwash streams. In many de­ valley at Stillwater, and at several posits, however, the sand and gravel points in the valley of the Minnesota occur as an intimate mixture. River, near Jordan, contains nearly as Some sands are nearly pure quartz much silica as the St. Peter formation. (silica sand) . One of the purest The upper part of the Jordan, which quartz-sand formations in the world has a total thickness of about 100 feet, is composed of sands with many re­ ( 99% Si02 ) is the white sandstone formation that crops out in the walls constructed quartz crystals. The crys­ of the Mississippi River valley, in the tals are hexagonal with short, sharp Twin Cities area. The sands of this pyramids on _both ends. Since quartz formation, called the St. Peter Sand­ is very hard (it will cut glass) such stone, have had a long and varied crystal sands are used for sandblast­ history. From the fact that only quartz ing. When the sand grains are forced grains are present in the formation, through the nozzle of a blasting hose one concludes that all the other less under high air pressure, the sharp resistant minerals were removed by edges and points of the crystals carve decomposition and disintegration prior inscriptions or other designs on gran­ to the deposition of the quartz sand. ite in a few minutes. It is used also Since the formation contains marine quite extensively for cleaning metal fossils, it undoubtedly accumulated in castings and for redressing the exterior an ancient epi-continental area. Its of stone buildings. Sands for such geographic distribution indicates that purposes are mined at Red Wing, similar sands were deposited over an Eggleston, and near the city of Jordan. area from eastern Colorado to central Kentucky and from Minnesota south­ Sands from both the St. Peter and ward into Oklahoma and Texas. Be­ the Jordan sandstone formations are cause of the high silica content of this used for many other purposes, and formation, it is mined at many places consequently they may be shipped and used as the chief raw material and sold under several names. A high­ in the manufacture of plate glass. A grade silica sand is glass sand to a typical installation is the glass plant glassmaker, steel sand to a steel of the Ford Motor Company in St. molder, grinding sand to a stone­ Paul, where the sand is mined by cutter, asphalt sand to a pavement underground methods on the land at contractor, facing sand to a concrete­ the plant. block maker, and furnace sand to a The Jordan sandstone that is ex­ foundryman. posed in the walls of the St. Croix Because of their many variations 30 MINNESOTA DEPARTMENT OF CONSERVATION

92 90

COMMERCIAL SAND If._ GRAVEL PITS IN MINNESO)A Legend,· @Pr//?cpo/ Co.mO?erc/o/ Sood i! GrC?ve/ P//-s, .!Vo. or P/rs in Areo md/cored Where Yore Thon One. + Srore Ot-r/?ed io 1937 L.eose L.vO?p ...5v/?7_, Per,n/~ · x {

96 ..90

Outline map of Minnesota showing commercial sand and gravel pits and state-owned pits. -Courtesy University of Minnesota Press. THE SANDS OF TIME 81 both physically and mineralogically, southeastern part of the state. the sands of Minnesota are adaptable Grinding and polishing sands are to many industrial uses. The foundries sharp, tough, hard sands free from require sands that vary from loamy clay or foreign material and sized for clay to clean silica sand or gravel, the use in sawing, cutting and polishing character of the material used de­ stone and for grinding and etching pending on the kind of metal to be glass. The size of the sand varies with poured, the size of the casting, the the character of the material to be surface desired and the place in the worked and the kind of work to be mold where the sand is to be used. done. A plant for processing such For core work a quartz sand free sands is operated at Mendota. from clay is preferred. Some organic Burnishing s~nd is a fine-grained, bonding material is added to the clean, tough, silica sand with grains clean sand. Greater permeability is as nearly round as possible used in obtained in this manner than is possi­ rolling down and burnishing gold ble where clayey or loamy sands are decorations on chinaware and proce­ used. A molding sand is a silicious lain. The sand should be very uniform sand having a clay content just suffi­ in size with the grains about seven­ cient to bind the sand grains together, thousandths of an inch in diameter but· not enough to fill the voids be­ ( 80 mesh) . The quartz grains of the tween the sand grains. When such a St. Peter sandstone are exceptionally mixture is moistened slightly, the mass well rounded and much of the sand may be molded into any form desired, is of the size indicated. retaining this form when dry. By far the greatest tonnage of sand The Hinckley sandstone, which is and gravel is used for constructional quarried extensively along the Kettle purposes. These sands are all of River near the city of Sandstone, glacial origin and were deposited as alluvial sediments in the major valleys contains strata that crumble somewhat or as products of glacial outwash at during quarry operations. The screen­ the margin of the retreating ice sheet. ings from such layers are composed Some deposits occur as alluvial cones of subangular, rough grains which known as kames and others are offer good attachment for bonding serpent-shaped ridges or eskers that material and are consequently used ~epresent deposits made .on the floor for refractory purposes in foundry of subglacial or superglacial streams. practice. The Galesville member of In most glacial streams the sands were the Dresbach sandstone, the Jordan, washed fre of clay before they were and the St. Peter sandstones, are used deposited. also in many of the foundries in the Pits and plants producing sand 32 MINNESOTA DEPARTMENT OF CONSERVATION

and gravel are so numerous through­ Paving out the state that a complete coverage Commercial ______223 ,7 40 97,720 Gov't contracts ______42,217 of the industry would be impossible 14,101 Grinding and polishing 1,603 1,509 without an extensive survey. The loca­ Fu~nace ------103 103 tions of the principal plants are shown Engine ------31,081 7,254 on the map. Filter ------664 2,158 The accompanying table shows the Railroad ballast ______171,949 37,928 Other uses ______26,399 amount and value of the sand and 5,358 GRAVEL gravel produced in Minnesota in 1944. Building Table showing the amount and value of Commercial 684,369 304,114 the sand and gravel produced in Minnesota Gov't contracts ______41,578 21,155 in 1944*. Paving SAND Commercial ______426,423 201,534 Use Short tons Value Gov't contracts ______5,287,990 363,129 Molding sand ------­ 18,502 $ 21,107 Railroad ballast ______2,128,350 584,914 Building purposes Other uses ______173,945 42,226 Commercial ______442,453 401,477 *U. S. Geological Survey, Mineral Yearbook, Gov't contracts ------2,786 1,017 1945. A Portland cement plant is soon to be erected in Minnesota. Marl Some Deposits Are 50 Feet Thick George A. Thiel Marl is a soft earthy material, bon dioxide gas is driven off and composed mainly of calcium this causes the water to become su­

carbonate ( CaC03 ), that is persaturated with the calcium carbon­ found as a freshwater deposit in lake ate. Thus the calcium compound is basins and bogs and in marshes or precipitated from solution and forms low areas that were once covered a scale in the kettle. In a similar man­ with water. Its composition is similar ner the lake water loses carbon di­ to that of limestone. It is usually oxide gas through the activity of grayish-white or buff, but darker col­ aquatic plants, such as Chara and ors may be seen where the marl is Zonotrichia. contaminated with peaty organic mat­ All green plants take in carbon ter. dioxide through their leaves and In hardness and consistency fresh stems. They utilize the carbon in marl resembles softened butter. In building up the complex molecules of some of the marsh deposits that are cellulose that serve as the basis of partially drained it is firm enough all plant . tissue. Where plants grow to be cut into blocks and handled in water that c0ntains excess calci­ with a shovel, and where compacted um which is held in solution by free under its own weight, marl has the carbon dioxide, the extraction of that consistency of common mortar when gas by the growth of the plants ready for use. In the shallow bays of causes calcium carbonate to be pre­ some lakes where deposition is still cipitated. in progress, the water may have a The source of the calcium in the milky white appearance due to the lake water is the glacial drift with its suspension of finely divided calcium heterogeneous mass of clay, sand, carbonate, that is kept agitated by gravel and boulders that cover most wave action. of the state with a mantle more than The manner of deposition of marl 100 feet in thickness. In some rng­ is similar to the deposition of the scale ions the drift lies in great level sheets in a tea kettle in which "hard" water or prames many miles in extent, is boiled. As the water is heated, car- while elsewhere it is piled up in a

33 34 MINNESOTA DEPARTMENT OF CONSERVATION great succession of hills, mounds and bonate from solution, it follows that ridges. Because of its origin this glac­ marl is always found in areas that ial debris contains an appreciable were once covered with water. (See amount of fresh or chemically unal­ Figure 1) . This does not mean that tered rock fragments. In some areas, all deposits are confined to the im­ pebbles of limestone are abundant; mediate vicinity of present-day lakes, in other regions, finely divided rock­ for during post-glacial time the reg­ forming minerals containing calcium ional ground-water level has been compounds constitute a major part of lowered and many old beach lines the drift. Soil waters percolating of lakes can be traced readily over through these limy clays and gravels areas that are now well-drained and carry with them dissolved carbon di­ cultivated land; marl also underlies oxide and the combined action of the partially drained swamps, and in dissolved gas and water leaches out some places it is found in the banks the soluble lime compounds from the of streams that have cut their chan­ soils through which it filters. The nels into a bed of marl as the outlet waters eventually reach the lake of a former lake or bog was lowered. basins through seepage springs on the There are hundreds ·of marl de­ floors of the lakes or as springs on posits in Minnesota, varying from less hillsides bordering the lake basins. than a foot to more than 50 feet in From the composition of the drift thickness. Deposits containing mil­ it has been commonly assumed that lions of tons occur at Star lake and the gray limy drift would be a bet­ its vicinity in northern Crow Wing ter source of marl than the red stony county. Another area of large deposits drift of eastern and central Minne­ occurs in a chain of lakes near Mon­ sota. However, a greater number of ticello and an equally extensive group marl deposits are found in the red of marl beds may be seen in a chain drift areas of the state than in the of lakes west and south of Clear­ regions of the gray drift. This is due water. In the northern part of the undoubtedly to the differences in tex­ state large deposits have been dis­ ture of the two types of drift. Even covered near Bemidji, near Backus though the gray drift contains a high­ and in Riley lake north of Taconite. er percentage of calcium carbonate, Some marl has been excavated and its texture is so fine-grained that it is dried to be used as part of the base relatively impervious, and conse­ in manufactured mineral stock foods quently the leaching action of ground and for chicken feed where it sup­ water is retarded. plants the crushed clam and oyster Since beds of marl owe their or­ shells commonly used for that pur­ igin to the precipitation of lime car- pose. The shell marl deposit that oc- MARL 35 curs near Swanville should make ideal nage of high grade marl is readily chicken feed. available, more should be used on A considerable tonnage of Minne­ sandy, siliceous farm lands in order sota· marl has been used as a neutral­ to obtain maximum benefits. izer of acid soils. Nitrifying forage Marl has been used for many years crops such as alfalfa and clover are in the manufacture of cement in In­ stunted or even inhibited in their diana and in Michigan. It has been growth by an acid soil condition. Sev­ reported recently that a larg-e up-to­ eral tons of marl per acre scattered date plant for making Portland ce­ over the soil soon neutralizes the ex­ ment will be erected in Minnesota in cessive soil acids. Since a great ton- the near future. In 1865 there was a 'gold rush' to Lake Vermilion.

Go/~ Silver and Other Metals

State Deposits Not Commercially Valuable George A. Thiel

An island in Lake Vermilion is economic value, but the long record called Gold Island. It was so nam­ of unsuccessful exploration is not ed during the 'gold rush' to the lake very encouraging. in 1865 when both gold and silver Silver minerals occur in veins were discovered there. Much of the near Pigeon Point, in rocks similar land east of the lake that subse- to those that have produced silver in quently became valuable for Ontario near the Minnesota iron ore, was staked for gold Minnesota's boundary. The veins also claims. In several years it Mineral contain small amounts of the was demonstrated that the Heritage sulphides of lead and zinc gold deposit on the island • • • (galena and sphalerite) , but was too lean and prospect­ At~ timagnesite ( MgC03 ) and brucite extraction on a commercial scale has (Mg(OH) 2 ). been developed to date. Minnesota has extensive supplies of wool rock.

Pea~ . Feldspar and Other Non--Metals

Will They Support New Industries? George A. Thiel PEAT of peat from seven to ten feet thick. The material called peat is partly Locally it may reach a thickness of decomposed and disintegrated veget- more than 20 feet. The deposits in the able matter that has changed chem- central and southern part of the state ically and physically but still retains are smaller and represent accumula- most of the carbon of the ,______, tions of grasses, rushes, cat- :>riginal plant tissues. Many Minnesota's tails and other marsh vegeta­ stems, roots, leaves and Mineral tion. seeds are still present in a Heritage Peat is excavated and used state of good preservation. extensively as a fertilizer From a geologic point of JV~ /Vu.ie filler and soil conditioner on view, peat is the first inter- ,______, farms, golf courses, gardens, mediate product in the series from nurseries and greenhouses; as packing vegetable matter to coal. material for plants, shrubs, fruit and There are hundreds of peat de- a variety of fragile objects; as litter posits in Minnesota and from a study for cattle and poultry; as surgical of the topography of the bottoms of dressings, and in the manufacture of the bogs, it is possible to divide them artificial wood, coarse woven fabrics, into two major types: (I) deposits tanning materials, nitrates, ammonium formed by the filling of shallow lakes sulphate, tars and dye-stuffs, etc. or ponds with plant remains and (2) Much of the peat in Minnesota is suit­ deposits which have been built up on able for fuel, but at present it is not flat marshy surfaces. Many of the de- in a position to compete with other posits in northern Minnesota are fuels. The estimated tonnage of air­ known as "muskeg" swamps which dried peat in this state is more than are largely made up of successive lay- six and one-half billion tons. ers of sphagnum or peat moss. They FELDSPAR are the largest, the deepest and Qf The feldspars are essentially alum­ the best quality in the state. A single inum silicates containing more or less deposit may cover an area of more potassium, sodium, and calcium. These than 50 square miles with a mantle minerals occur mainly in granite, but

39 40 PEAT, FELDSPAR AN DOTHER NON-METALS the soda-lime feldspars are constitu­ ville, Galena and Oneota dolomites ents of darker colored igneous rocks, are wool rocks. such as the gabbro that crops. out in A plant at Mankato uses an argil­ the vicinity of Duluth. In exceptionally laceous dolomite near the base of the coarse grained granitic dikes called Oneota formation and the rock wool pegmatites, the feldspar grains may plant at Red Wing has quarried and be from three or four inches to more used many tons of the St. Lawrence than two feet aoross. Such feldspar dolomite. is blasted from the rocks and finds a There is virtually an unlimited sup­ ready market. ply of suitable wool rock in the sedi­ Crushed and ground feldspar is mentary strata of southeastern Minne­ used in the manufacture of glazes and sota. metal enamels. It is used also as a POTASH-BEARING MINERALS flux in the manufacture of glass and in The Franconia formation that oc­ the ceramic industries where it is curs at or near the surface along the mixed with clays to make porcelain valleys of the St. Croix and Missis­ ware, china, pottery, earthenware, wall sippi rivers contains an appreciable and floor tile and other clay products. amount of the mineral glauconite. This The only feldspar mine in Minne­ mineral is essentially a hydrous sili­ sota is located in the Northwest Angle cate of iron and potassium. At some northwest of Lake of the Woods. The places the glauconite contains seven hand-picked ore is carried by barge or eight percent of potash. Although to a mill at Warroad where it is this potash is only slightly soluble in crushed and bagged for shipment to water, small amounts of it are avail­ various manufacturers. able for plant use. For this reason WooL RocK glauconitic sands are used as a fer­ Fibrous insulating materials made tilizer filler with some success. Because from rock is known in industry as of its base-exchange characteristics, rock wool. The raw material common­ glauconite is used extensively also for ly used for making the fine glassy water softening. There are accessible fibers is a clayey limestone or dolo­ locations near rail or river transporta­ mite. If such rocks have a carbon tion where millions of tons of highly dioxide content of 20 to 30 percent, glauconitic sands and silts can be ex­ they can be satisfactorily melted and cavated in east central and southeast­ blown into wooly fibers. Analyses of ern Minnesota. Minnesota limestones and dolomites SULPHUR COMPOUNDS indicate that most of the St. Law­ There are no deposits of pure sul­ rence dolomite which is about 30 feet phur known in Minnesota; however, thick and thinner layers in the Platte- compounds of sulphur and iron are THE CONSERVATION VOLUNTEER 41

common sources of sulphur. If at encountered in the glacial drift in some future date large quantities of numerous areas. It occurs in pockets sulphuric acid are needed for leach­ that "bounce the tools" as well-drill­ ing and concentrating low-grade ores ers penetrate them. Occasionally it or for other chemical processes, sul­ throws out quantities of mud and phides of iron might be obtained in other rock debris. These "puffs" are of commercial amounts at· several points short duration and further drilling in the region of Long Lake, about 12 does not increase the How of gas. The miles southeast of Aitkin. Preliminary highest pressure recorded is 22 drilling has demonstrated the presence pounds. Such pressures subside in a of both pyrite and pyrrhotite in the few hours, but small quantities of gas graphitic slates of that area. Pyrite, may issue from the wells for many FeS2 (Fool's Gold) is a very common years. No methane has been encoun­ mineral and it is present· in small tered in holes drilled into the bed­ amounts in a great variety of rocks; rock beneath the glacial drift. however, few large deposits are There has been considerable drilling known. for oil in Minnesota beginning as ';RAPIDTE early as 1887. However, the age and The graphite in metamorphic rocks structure of the rocks are such that such as slate and schist is a residue dil­ commercial production is very doubt­ rived from the cellulose of plant tis­ ful. There has been an occasional leak sue that was deposited in the sedi­ from some storage tank of gasoline or ments from which the rocks were fuel oil into the soil and glacial drift, formed. Graphitic slates are very com­ which created much unjustified hope mon in northern Minnesota and at of commercial accumulation of petro­ several places test pits have been ex­ leum. cavated in an attempt to locate mater­ ial of commercial grade. A pit north­ SALT west of Mahtowa is in the Carlton No deposits of rock salt are known slates; one on Pigeon Point is in gray in Minnesota, but many wells produce quartzite and another in that area salt water. This is especially true in has small quantities of graphite in the the Red River Valley region where "red rock." No commercial deposits salt was obtained from brine as early have been found. as 1884. Although there are numerous GAS AND OIL salt springs, no large brine industry Methane or marsh gas has been has developed. . I