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Home , Conchoidal fracture, Diorite, Erin (color), Pegmatite, Phyllite, Xenolith

ROCKS ... and how to identify them THE CYCLE

A tutorial program offered to you by the Applied Science Rocks are naturally occurring combinations or coherent Department of Glendale Community College aggregates of , fossils or other hard materials. They are classified by the way in which they form. The presented by: three rock types are: igneous, sedimentary and Susan Celestian – Curator of the Arizona Mining and metamorphic. Museum Stan Celestian – Photographer and Instructor All rocks on Earth are locked into a system of cycling and re-cycling known as the . (*) © copyright 2006

This is your cue to advance to the next slide. (*)

THE ROCK CYCLE IGNEOUS ROCKS IGNEOUS ROCKS are “born of IGNEOUS fire”. In other words, they w ea vent th er were once molten and upon in li g, th i t f r g ic a land s n a n urface cooling, the (molten ti t s l io p e n or m ta e, ti rock) crystallized into solid r on u conduit s

s es m on e pr i rock. Igneous rocks may , lt magma t in g ea h form deep inside the Earth or at the Earth’s surface when a

METAMORPHIC SEDIMENTARY erupts. (*) , transportation, lithification

heat, pressure, ions Anatomy of a Volcano (*)

CLUES TO IGNEOUS ROCKS IGNEOUS ROCKS

COLOR LIGHT COLORED INTERMEDIATE DARK COLORED VERY DARK COLORED COLORED Rapid cooling near or at the TEXTURE Ultramafic Earth’s surface, produces COARSE- : : : : Slow cooling deep beneath the GRAINED Can see . Usually Can see crystals with Can see crystals — lots of Composed of 90- many small crystals that are (You can see gray or pink. Can see somewhat more light colored flat shiny cleavage surfaces. 100% - gray, glassy grains. grains than dark Earth’s surface allows crystals different Can see feldspar - pink, colored minerals. A mix of light Usually black to greenish not readily seen by the minerals) buff, or white. and dark but with no quartz. Salt black. : Composed of pre- to grow to large size (1/8” or & pepper appearance. unaided eye. This group of dominately

FINE- more). These crystals are : : : : igneous rocks is called GRAINED Usually gray, pink, Light to dark gray. Normally has Usually black or rust . Composed of pre- pastel. Might see small small black crystals May have some or lots of (You can NOT dominately easily visible and distinguish EXTRUSIVE and are typically clear, rectangular crystals. gas bubble holes, some (such as ) see crystals, for Sometimes banded. holes may be filled. May this group of igneous rocks as volcanic in origin. Cooling the most part) see small grains. : Black, red, green, may be so rapid that crystals GLASSY INTRUSIVE. PERLITE: Usually pearly gray. May contain Apache Tears. do not have a chance to form PUMICE: LOTS of gas bubble holes, very lightweight, will float on water. Abrasive. and instead a glass is PORPHYRITIC ALL CRYSTALLINE IGNEOUS VARIETIES may exhibit porphyritic texture produced. (*) (2 grain sizes)

TUFF: Compacted volcanic fragments generally less than 4mm diameter (ash) FRAGMENTAL VOLCANIC : Mixed tuff and angular large (>32mm diameter) fragments (*) AGGLOMERATE: Mixed ash and rounded/sub-rounded large (>32mm diameter) fragments Granite - intrusive Granite - intrusive Graphic Granite quartz GRANITE is a coarse to medium- (*) grained rock that forms from the cooling of magma deep within the Earth (intrusive). It feldspar is made up mainly of varying amounts of the minerals: mica quartz, , , biotite and hornblende. The Porphyritic name is from the Latin granum, for “grains”. feldspar (*)

Granite - intrusive Pegmatite a Special Case Diorite - intrusive are classified as intrusive igneous rocks, but there is a DIORITE is very similar to difference. They are VERY feldspar coarse grained and strictly granite, but is distinguished speaking are not crystallizing in the hand specimen by the out of a magma. absence of visible quartz. The coarse grained nature is

mica the result of growth in aqueous solutions rather than Generally it has a salt and in the molten liquid state. pepper appearance (about The resulting freedom of ion ½ black and ½ white). quartz motion allows the crystal to grow much larger in a shorter length of time. (*) feldspar biotite (*)

Gabbro - intrusive Peridotite - intrusive

GABBRO is a coarse-grained PERIDOTITE or is rock that is high is & composed of 90-100% magnesium-bearing minerals olivine. As a result it is (, amphiboles, characteristically - feldspar, olivene). in color. The rocks will be dark in color, somewhat heavier than granitic rocks and devoid of This material is thought to quartz. have originated in the upper Black minerals are primarily (like mantle of the Earth. (*) hornblende) and plagioclase feldspar. (*) Rhyolite – extrusive Rhyolite – extrusive

RHYOLITE’S name comes from sized crystals develop. The the Greek rhyo, from rhyax, volcanoes that produce “stream of lava”. It is formed rhyolite are very explosive when molten rock with the varieties such as Mt. St. same composition as a high Helens, Krakatoa and silica granite oozes (rhyolite is O’Leary Peak (AZ). This is another sample of rhyolite. VERY viscous and does not Frequently it is banded due This has a crystal of that really flow) to the Earth’s to flow alignment of different grew after the rhyolite was surface; and therefore cools associated minerals (quartz, deposited. (*) This is an example of quickly so only microscopic- feldspar, mica, and banded rhyolite. (*) hornblende). (*)

If you look closely, you might see tiny clear of feldspar. (*)

Andesite - extrusive Basalt - extrusive

ANDESITE is the fine- BASALT occurs as thin to is dark, fine-grained and massive lava. flows, often vesicular (having gas grained equivalent of pockets). The pockets may DIORITE. It tends to be sometimes accumulating to be filled with secondary thicknesses of thousands of a darker gray than minerals, e.g. quartz, zeolite feet and covering thousands minerals, calcite, , etc. hornblende rhyolite and is often of square miles. The and then it is called phenocrysts (*) porphyritic, with visible volcanoes that produce amygdaloidal (a-mig-duh-loy- hornblende. basaltic are relatively dal) basalt. quiet, such as the Hawaiian The name may have originated Islands volcanoes. Basalt with Pliny who used the Ethiopian word basal for iron- bearing rocks. (*)

Basalt - extrusive Basalt - extrusive Vesicular (Scoria) Volcanic Bomb (*)

Peridotite xenolith

Basalt (*)

Gases released near the surface of a lava flow create bubbles or vesicles that are “frozen” in stone. (*) Amygdaloidal Peridotite (*) (*) Basalt - extrusive Obsidian - extrusive Pahoehoe is a feature that forms on the OBSIDIAN is volcanic glass (an surface of very fluid have cooled so quickly that acrystalline “solid” –actually a basalt flows. Much the minerals could not like the skin on a bowl supercooled liquid). Its develop and crystallize. of tomato soup – the glassy, lustrous and vary from black to red, surface in contact with sometimes banded black & red (mahogany), the air begins to appearance makes it rather gray, green, iridescent, crystallize, while the easy to distinguish from all snowflake. fluid lava below other rocks. It is composed Apache Tears are little nodules continues to flow. This of the elements that make of obsidian. drags the upper, still quartz, feldspar and iron/ plastic, surface into a magnesium minerals that series of smooth wrinkles. (*)

Obsidian - extrusive Apache tear Perlite - extrusive Flow banding PERLITE is a light gray volcanic Apache Tear glass, having numerous concentric cracks which give rise to a perlitic or onion skin structure. It is generally of rhyolitic composition. It also exhibits a pearly luster.

Apache Tears are some times found embedded in perlite.

Snowflake

Pumice - extrusive Tuff - extrusive

PUMICE is highly vesicular Tuff is the accumulation of ash (i.e. it has lots of gas and small pyroclastic debris bubble holes) and is of (<4mm). Thick beds may rhyolitic composition. form for many miles around a very explosive volcano, Due to the many small such as Mt. St. Helens. holes, it is lightweight Often, when the material is still and will often float in hot upon deposition, it welds water. into a very hard rock. Volcanic Breccia - extrusive SEDIMENTARY ROCKS

VOLCANIC BRECCIA is SEDIMENTARY ROCKS are composed of particles pyroclastic (fire-formed derived from pre-existing rocks or by the fragments) and forms in of minerals that were held in solutions. explosive eruptions. It is A general characteristic of this group is the layering or a mix of large angular stratification, as seen in the outcrop. fragments and small ash. Those sedimentary rocks that are CHEMICAL sedimentary rocks are the Often, the material is hot composed of particles of pre-existing result of either precipitation of solids when it comes to rest rocks are considered FRAGMENTAL from solutions (like salt from water) or or CLASTIC. These fragments show by organic process, like shells from and cools (welds) into a evidence of transport – rounding of the marine organisms. very hard rock. grains and size sorting.

CLUES TO Breccia - fragmental SEDIMENTARY ROCKS

FRAGMENTAL: Composed of pieces of rocks and minerals A BRECCIA is made of varying sizes of angular fragments

BRECCIA: Composed of large angular pieces and clay cemented together. The LARGE PIECES CONGLOMERATE: Composed of large rounded pieces and name is from the Italian word (Boulders,cobbles, clay pebbles) for “broken stones” or

“rubble”. SMALL PIECES : Looks sandy (may “shed” sand grains), feels Many form as the result of fault (sand) rough (like sandpaper); may be tan, white, red, gray. movement; others form as the result of rapid and short : Has very thin layers; often black. May have fossils — VERY SMALL PIECES usually impressions (no shell, but indentation with pattern of transportation, such as (clay, silt, mud) shell) or carbonized film (as for plants). Has a dull luster. Is landslides. soft. When tapped with a rod or on a table, it generally makes a dull thunk.

Conglomerate - fragmental Sandstone - fragmental SANDSTONE is made up of CONGLOMERATES are very fine-grained particles (1/16 – similar to , but the 2 mm). The sand grains fragments are rounded. The (often quartz) are commonly name is from the Latin cemented by silica, conglomeratus for “heaped, carbonates, clay or iron rolled or pressed together”. oxides. Sandstone is identified by its sandy texture Coconino Sandstone, These rocks form in alluvial the result of a Permian – which often translates into age coastal dune field fans, stream beds and a gritty feel. pebble beaches. Environments in which form include beaches, sand bars, deltas and dunes. MORE CLUES TO Shale - fragmental SEDIMENTARY ROCKS

SHALE is a very common rock CHEMICAL: Rocks are crystalline

made of silt and clay sized LIMESTONES: Composed of calcite and all WILL FIZZ vigorously in acid Crystalline — Looks sugary, usually gray or tan particles. It is generally very Fossiliferous — Contains seashells (usually) or other aquatic organisms Travertine — Looks sugary with bands of various colors thin-bedded and splits along Chalk — White and soft (comes off on hands) Coquina — Contains almost nothing but seashells or seashell fragments the bedding planes. In fact, : Cryptocrystalline QUARTZ Very fine — can NOT see crystals the name is probably from Waxy luster Black shale, deposited in a offshore Conchoidal (breaks like glass) the Old English scealu, “shell basin in a Middle Cambrian sea. Very hard — will easily scratch glass Wheeler Shale with trilobite fossil May be ANY COLOR (Red = , Black = , includes or husk”. Normally gray to Silicified ) (Elrathia kingii) GYPSUM: White, gray, clear black, shale may be brown to Very soft — you can scratch with fingernail dark red, depending on the Fish scales Clear sheets, fibrous or sugary ROCK SALT: White to clear — cubic shape amount of included iron Soft — you can scratch it with fingernail Tastes like table salt (IT IS TABLE SALT!) oxide. COAL: Black; Brittle; Lightweight May contain plant fossils form in quiet environ- Varieties: peat, lignite (incl. jet), sub-bituminous, bituminous

ments, such as lakes, DIATOMITE: White Very soft (comes off on your hands) swamps, deltas and offshore Utah Lightweight marine. Will NOT fizz in HCl acid (unlike chalk)

Limestone - chemical Uses: LIMESTONE is composed LIMESTONE - chemical Coquina  Manufacture of and primarily of calcite. Generally Portland cement & to Crystalline it is dense, fine-grained, and neutralize smokestack usually white to dark gray. Its gases. most distinguishing feature is  Finely ground, used as a its in weak functional filler in products such as paint, countertops hydrochloric or acetic acid & plastics. Pleistocene, Rocky Point, accompanied by brisk  The dust on chewing gum is Mexico effervescence. ground limestone. Redwall Limestone Mild abrasive additive to Travertine The environment of deposition if  Mayer, AZ toothpaste. generally warm, shallow seas.  Soil conditioner Therefore, marine invertebrate  Flux in processing iron and fossils are common. copper ores.  Building and ornamental Fossiliferous stone.

GYPSUM - chemical Satin Spar Alabaster CHERT - chemical GYPSUM ( sulfate) is found in geographically wide- CHERT is crypto-crystalline spread deposits resulting from quartz. It is often the result of the evaporation of a body of the dissolution of Selenite water, such as ocean basin or and is sometimes found in playa lake. extensive beds, such as the It is soft (H=2) & usually white to novaculite of Arkansas. gray. Three varieties are: It has waxy luster, is translucent Alabaster, Satin Spar and and conchoidally. Selenite. Chert can be any color, but Gypsum is mined for use in extensive beds are generally wallboard and plasters, as an white to gray. agricultural amendment and to control the set/cure time of Gypsum & (water-less Portland cement. calcium sulfate), Carlsbad, NM ROCK SALT - chemical COAL - chemical

ROCK SALT (halite – sodium COAL is considered a rock, chloride) is also a deposit although it is not composed of resulting from evaporation of minerals, but rather the a marine basin or playa lake. decomposed remains of large It has cubic cleavage and tastes volumes of vegetation that salty. accumulated in a wet, low Rock salt is used as a source of oxygen environment, such as a chlorine and sodium, as a swamp or marsh. food supplement, in water Peat, Lignite and Sub-Bituminous softeners and as a road de- & Bituminous are sedimentary Coal (sub-bituminous) out of the Cretaceous Dakota icer. Formation of north-eastern Arizona. varieties of coal and are used as fuels.

Halite Trona, CA

DIATOMITE - chemical METAMORPHIC ROCKS METAMORPHIC ROCKS have changed (meta)theirform(morphic). Under DIATOMITE, also known as the influence of heat, pressure and fluids, pre-existing rocks are modified diatomaceous earth, is in form and even in internal atomic structure to produce new rocks stable at the new conditions. This is done within the solid state, i.e. without composed of the siliceous melting. shells of microscopic alga Changes that occur include: increase in grain size, new minerals and called diatoms. It is light (parallel alignments). weight and is generally white. Diatomite is used as an Metamorphic rocks that exhibit Metamorphic rocks composed of abrasive, insecticide, filtering parallel alignments of minerals that are not elongated San Manuel, AZ minerals are called or flat, do not exhibit parallel medium, and paint “flattener”. FOLIATED. In these rocks, alignments and are called the minerals all line up NON-FOLIATED. perpendicular to the exerted pressure.

SLATE - foliated CLUES TO METAMORPHIC ROCKS is derived from shale. It is a dense, microcrystalline rock, but one in which FOLIATED: Rocks have layers or banding parallel planes are very

SLATE: Rock breaks into very thin layers evident in its slaty foliation – Beginning to look polished; Is harder than shale a feature resulting from the Cannot see crystals Black , gray or red alignment of clay and mica PHYLLITE: Like slate, but shinier (“phyllitic sheen” — similar to satin) minerals,which allows it to : Very shiny — you can SEE CRYSTALS (usually MICA) split readily into sheets. It Is layered may be gray, black, green or May have crystals (of garnet, tourmaline, etc.) growing with the mica red. : Crystalline Uses include roofing, flagstone, Note the relatively dull luster of slate. Black & White BANDING (due to segregation of minerals) pool table tops and “blackboards”. PHYLLITE - foliated SCHIST - foliated SCHIST is medium to coarse- PHYLLITE is somewhat more grained, crystalline, with metamorphosed than slate. prominent parallel mineral orientation. Typically, it is The platy crystals of mica predominately muscovite mica, have grown and the rock which lends a silvery white to Crumpling of schist due to displays a subtle, satiny pressure and collapse of gray sparkly appearance. It is mica crystals shine referred to as “phyllitic not unusual for accessory sheen”. The name comes minerals (such as , from its leaf-like (many fine staurolite, tourmaline) to grow in Note the phyllitic sheen. the rock. layers) appearance. tourmaline Schist is added to clay mixtures as porphyroblast – a strengthening material in note alignment vitreous pipe (red sewer) and garnet clay roof tiles. porphyroblast

Gneissic granite – separation of dark of shale & light minerals is just beginning GNEISS - foliated SHALE is the most common .

Well banded gneiss Through the agents of metamorphism it changes to rocks that GNEISS formed under are stable at higher temperatures and pressures. conditions of high temperatures and These changes take place in the solid state. Augen = quartz pressures at great depth pebble resistant to during regional compression metamorphism. It is GRANITE characterized by foliation expressed as MELTING Produces black and white banding. GRANITE

Because the rock Augen Gneiss becomes plastic, the Slate Schist Phyllite banding is often Shale Gneiss

contorted (squiggly). kink in gneiss Increasing Temperature and Pressure

CLUES TO THE ROCK CYCLE METAMORPHIC ROCKS

IGNEOUS

w ea th NON-FOLIATED: Shows NO layers or banding er in li g, th i t f r g ic a MARBLE: Sugary looking n a n ti t s l io p e n or Will fizz in HCl (acid) m ta e, t r ion Often is multi-colored, may be white u s

s Soft — will not scratch glass es m e pr ion , lt t in g : Very dense ea h MAY look a bit sandy Very hard — will easily scratch glass METACONGLOMERATE: Looks like sedimentary conglomerate, METAMORPHIC SEDIMENTARY BUT it is harder (BREAKS THROUGH PEBBLES) and often the

weathering, transportation, pebbles are squished & aligned (it is at this point foliated) lithification SERPENTINITE: Composed of members of the serpentine family (includes chrysotile asbestos) Generally light greenish gray to greenish black Waxy luster heat, pressure, ions Often exhibit curved and slickensided surfaces MARBLE – non-foliated MARBLE is metamorphosed QUARTZITE – non-foliated limestone or dolomite. The colors can vary from pure white to gray, green, yellow, brown, black, red or any combination QUARTZITE is metamor- thereof, depending on the phosed quartz sand- ‘impurities’ in the parent limestone. Bands or streaks stone. It is a very result from plastic flow during dense,durable, massive, Aguila, AZ extreme deformation, due to high pressure and temperature. microcrystalline rock (but Hewitt Canyon, AZ It is calcite or dolomite and will fizz in still may retain a slightly weak acids. sandy look). It can be Marble is used for building facades, floors, countertops, statuary, any color, but tends to be landscaping, paving/roofing, white, tan or pink. poultry grit, and as filler/extender for paint, plastics, and adhesives.

METACONGLOMERATE – non-foliated

SERPENTINITE – non-foliated Conglomerate METACONGLOMERATE is metamorphosed SERPENTINITE is composed of conglomerate. It retains its pebbly appearance, but one or more minerals in the while a sedimentary serpentine family. It is conglomerate will break common where wet around the pebbles, a or mantle rocks are metaconglomerate will metamorphosed, such as at break through the pebbles. convergent boundaries. Its green colors, waxy luster, If temperatures are high Chrysotile enough in the presence of asbestos often associated asbestos and common slickensided pressure, the pebbles may Salt River Canyon, AZ surfaces are clues to its become squished or identity. flattened and will be elongated parallel to each other (becomes foliated).