The Franklin Marble: One of New Jersey’S Most Famous Geologic Formations

New Jersey Geological and Water Survey Information Circular The Franklin Marble: One of New Jersey’s Most Famous Geologic Formations Introduction 0 5 10 Miles NY Sussex County Few rocks in New Jersey are as attractive or as well known as the Franklin Marble, which displays a Franklin virtual rainbow of colors from white, PA to light gray, pale pink, orange, pale Limecrest green, or pale blue. Samples of Franklin Quarry Marble are displayed in many museum exhibits nationally and internation- ally because of its importance as host rock for the world-famous zinc-iron- manganese deposits at the Franklin and Sterling Hill mines in Sussex County. These deposits contain more than 350 minerals, of which 90 are fluorescent. If New Jersey Highlands area of ever there were a contender for the offi- detail cial state rock of New Jersey, Franklin Marble would certainly be among those at the top of the list. Early in the study of the state’s geologic history, all marble was simply called white or crystalline limestone (Cook, 1868). The name “Frank- lin white limestone” was first intro- Figure 1. Distribution of the Franklin Marble (shown in blue) and other uncorre- duced by Wolff and Brooks (1898) for lated marble deposits (shown in red) in the New Jersey Highlands. marble at the zinc deposits in Frank- lin Borough. This was later shortened the area, where it forms a nearly continu- known. As a result, Franklin Marble was to “Franklin limestone” on one of the ous 21-mile-long belt in Sussex County. quarried extensively during the 20th cen- early state geologic maps of New Jersey Marble also crops out in small, detached tury, although most of the quarries are no (Lewis and Kümmel, 1910-1912), and bodies in the southwestern and eastern longer in operation. Less well known, but in contemporary publications of that Highlands. Although these rocks are sim- equally important, was the use of Frank- time (for example, Spencer and others, ilar in most respects to Franklin Marble, lin Marble from the Limecrest Quarry 1908; Kümmel, 1940). New Jersey geologists are unable to positively cor- (fig. 1) in Sussex County, by Thomas Zinc Company geologists (Hague and relate them to the marble at Franklin. Edison in 1906 as pulverized lime in the others, 1956) referred to the marble Franklin Marble is characteristically making of cement. at the Franklin mine as the “Franklin medium to coarse-grained and texturally Marble”. This is perhaps the earliest use massive (fig. 2). It consists mainly of Despite nearly a century and a half of the name in the literature, and it has the mineral calcite (calcium carbonate), of scientific inquiry into the Franklin since been retained as a formal name but may also contain varied amounts of Marble, some very important questions on the bedrock geologic map of New other minerals such as graphite, phlogo- remained unanswered. These included: Jersey (Drake and others, 1996). pite mica, and various silicate and non- 1) the age of the marble; 2) the condi- silicate minerals. Marble is a metamor- tions of its metamorphism during burial Franklin Marble phic rock. That is, it must be converted in the Earth’s crust; 3) the specific type or metamorphosed from a sedimentary of environment in which it formed; and Marble in New Jersey occurs only precursor of similar composition. 4) its geologic relationship to other rocks in the New Jersey Highlands Province in the New Jersey Highlands. Answers (fig. 1) where it makes up about two Because of marble’s high calcium to these questions were obtained between percent of the rock exposed there. It is content, its importance as lime to con- 2004 and 2009 by the author, in col- most abundant in the northwest part of dition agricultural soils has long been laboration with other scientists, through the marble, as well as recent geologic mapping by the New Jersey Geologi- cal and Water Survey, combined with detailed geochemical and isotope studies of the bedrock, some of the gneisses and marble were interpreted as forming in an ocean setting in a basin located off the ancestral North American continental margin (Volkert and others, 2010). A chain of volcanoes similar to those of the present-day Cascade Mountains in the Pacific Northwest was situated farther to the east (fig. 3). The carbon and isotope values (Peck and others, 2006), and the strontium isotope values of calcite in the marble showed they formed in seawater. Additionally, fossil colonies of single-celled algae known as stromatolites were discov- ered in the marble (fig. 4), confirming that it formed in an ocean environment. During the collision of eastern North Figure 2. Outcrop of fairly typical coarse-grained Franklin Marble from near Franklin, America and ancestral South America Sussex County. Lens cap for scale. Photo by Rich Volkert. at about 1050 million years ago, rocks in the New Jersey Highlands were detailed geologic mapping and stud- recrystallized into the metamorphic buried deep in the Earth’s crust where ies using geochemistry, combined with rock marble. Many of the 350 minerals they were metamorphosed. They were interpretation of the isotopes of carbon, in the marble were formed at this time, later uplifted and are now exposed at strontium and uranium-lead. either from layers of different chemi- the surface following erosion of the cal composition or from metamorphic rocks that once covered them. Age and Origin of the Marble fluids intruded into the rock about 1000 million years ago (Volkert and others, It’s not often that geologic condi- The age of the Franklin Marble 2005). tions combine to form something as could not be determined directly unique and famous as the zinc-iron- because the rock lacks appropriate The environment in which the manganese deposits in Sussex County minerals for dating. Instead, volcanic Franklin Marble formed was deter- hosted by the Franklin Marble. In fact, gneisses lying directly beneath and mined using several lines of evidence. only one other location in the world, above the marble were dated at 1294 Based on previous geologic studies of Långban, Sweden, has a marble-hosted and 1299 million years using isotope analysis of uranium and lead (Volk- ert and others, 2010). Because these gneisses formed contemporaneously with the marble, an age of about 1295 million years was interpreted for the time of deposition of the limestone precursor of the marble. Uranium-lead isotope analysis also provided a precise age of 1050 million years for the time of metamorphism from limestone into marble. Using isotopes of carbon to calculate the equi- librium relationship betweem calcite and graphite in marble, a temperature of 769oC (about 1,400oF) was determined for the peak of metamorphism (Peck and others, 2006). During this metamorphism, the precursor lime- Figure 3. Simplified diagram showing back-arc basin in which the limestone precursor stone was buried to a depth of about of Franklin Marble was deposited. Basin formed between the continental margin to the 13 miles in the Earth’s crust where it west and a volcanic arc and subducted ocean crust (lavender) to the east. deposit of comparable rarity. New Jersey is fortunate in that its geologic past has provided us with one of the world’s geologic masterpieces. The next time you are looking for some adventure, consider going to the Ster- ling Hill Mining Museum (www. sterlinghillminingmuseum.org) at Og- densburg Borough and the Franklin Mining Museum at Franklin Borough, to see these fascinating deposits and the Franklin Marble, one of the state’s most famous geologic formations. References Cook, G.H., 1868, Geology of New Jersey: New Jersey Geological Survey, 900 p. Drake, A.A., Jr., Volkert, R.A., Monte- verde, D.H., Herman G.C., Hough- ton, H.F., Parker, R.A., and Dalton, R.F., 1996, Bedrock Geologic Map of Northern New Jersey: U.S. Geo- Figure 4. Wavy-laminated, dark gray colonies of stromatolites (beneath ruler) in Frank- logical Survey Miscellaneous Inves- lin Marble. Photo by Brett Kent. tigations Series Map I-2540-A, scale 1:100,000. Jersey: U.S. Geological Survey Atlas Folio 161, 27 p., scale 1:62,500. STATE OF NEW JERSEY Hague, J.M., Baum, J.L., Herrman, Chris Christie, Governor L.A., and Pickering, R.J., 1956, Volkert, R.A., Aleinikoff, J.N., and Kim Guadagno, Lieutenant Governor Geology and structure of the Frank- Fanning, C.M., 2010, Tectonic, lin-Sterling area, New Jersey: Geo- magmatic, and metamorphic his- Department of Environmental Protection logical Society of America Bulletin, tory of the New Jersey Highlands: Bob Martin, Commissioner v. 67, p. 435-474. New insights from SHRIMP U-Pb geochronology, in Tollo, R.P., Bar- Water Resources Management Kümmel, H.B., 1940, The Geology of New tholomew, M.J., Hibbard, J.P., and New Jersey Geological and Water Survey Jersey: New Jersey Department of Con- Karabinos, P.M., eds., From Rodinia Karl Muessig, State Geologist servation and Economic Development, to Pangea: The Lithotectonic Record Bulletin 50 Geologic Series, 203 p. of the Appalachian Region: Geo- J DE P N L GEO OGI Y C A logical Society of America Memoir E L S R S E U J R V W Lewis, J.V., and Kümmel, H.B., 1910- 206, p. 307-346. E E Y 1912, Geologic map of New Jersey: N New Jersey Department of Conser- Volkert, R.A., Zartman, R.E., and Moore, 18 3 5 vation and Economic Development, P.B., 2005, U-Pb zircon geochro- Atlas Sheet 40, scale 1:250,000. nology of Mesoproterozoic posto- Prepared by Richard A. Volkert rogenic rocks and implications for 2013 Peck, W.H., Volkert, R.A., Meredith, post-Ottawan magmatism and metal- M.T., and Rader, E.L., 2006, Calcite- logenesis, New Jersey Highlands and Comments or requests for information are graphite thermometry of the Franklin contiguous areas, USA: Precambrian welcome.

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