White Marble Mostly bright white. Made of medium-sized crystals that glitter in sunlight. You can scratch it with a nail or knife,and the rock bubbles in vinegar or acid. White ChertMostly white, sometimes chalky looking or smooth.Broken edges may be sharp or scalloped. Nail doesnt scratch it and it does notbubble in vinegar. White Granite Mostly white or yellowish, with dark specks. Small broken crystal surfaces shine in sunlight. Nail doesnt scratch it and it does notbubble in vinegar. Dolostone Mostly light gray. You can scratch it with a nail or knife.Only powdered rock bubbles in vinegar or acid. Limestone Light to dark gray. You can scratch it with a nail or knife. Rock bubbles in vinegar or acid. Gray Slag Light to dark gray or yellowish. Dull to somewhat glassy.Usually has lots of rounded bubble holes.Some spots bubble in vinegar or acid, but most place do not. Quartz (from Pegmatite) Cloudy white, a bit pinkish, or clear. Looks a bit like broken glass. Nail doesnt scratch it and it does notbubble in vinegar or acid.
Quartzite pebblesWhite (also yellowish or light brown).Can see large sand grains -- sometimes crumbly. Nail doesnt scratch it and it does notbubble in vinegar or acid. Slate Dark gray, looks silky in the sun. Breaks into mostly flat pieces. Basalt or "Trap Rock" Dark gray, dull looking. Mostly fine-grained, but may contain scattered larger crystals. Breaks into chunks with smooth sides. Scoria (type of Basalt) Black or reddish. Lots of rounded bubble holes. Doesnt float in water. Slag (human-made lava) Black, whitish, or reddish.Some rounded bubble holes, but mixedwith crumbly places and smooth glassy spots. Some parts fizz in acid. Obsidian or Volcanic Glass Draws no line or a white line on the sidewalk.Hard to break -- if you do break it, sharp edges can cut you! CoalDraws a black line if you scrape it on the sidewalk.Pretty easy to break into a mix of blocky,crumbly, and powdery pieces that leave your hands dirty!
Gabbro Looks dark gray, but really a mix of black and light crystals. Small broken crystal surfaces shine in sunlight. Scoria (a type of Basalt) Reddish or black. Lots of bubble holes. Doesnt float in water. Pink Quartzite Pink, sometimes yellowish. If you look closely, you may see some pieces are made of sand-sized grains. Red Granite Mostly reddish pink, but... ...if you look closely, youll also see gray and purplish spots. Saprolite ("weathered" granite) Most pieces stained rusty red or coated with a dark reddish crust. If you look closely, youll see pink, gray, and darker crystals (like in Red Granite). Pegmatite (like granite, but with really big crystals!) Pink pieces mixed with whitish, gray, and silvery pieces. Most pieces are made of only a few large crystals. Quartz rock Most pieces stained rusty red or yellowish, or coated with rusty-red powder. If you look closely, youll see small, pointy crystals and thinly layered rock. Brown ChertMostly brown, but mixed with cream and darker colors. Some sides look really smooth, but freshly broken edges may be sharp! Nail doesnt scratch it (but may leave a
dark line). Pumice Tan or gray. Lots of bubble holes. Feels very light in weight, for a rock. Dry pieces often float in water. Quartzite pebbles Brownish, yellowish, or white. Can see large sand grains in some pieces - - sometimes crumbly. Nail doesnt scratch it (but may leave a dark line). Brown Quartzite pebbles Brownish, tan, white, or reddish. Outside very rounded and smooth. Broken edges look glassy and may be sharp. Nail doesnt scratch it (but may leave a dark line). Mica (in Pegmatite) Thick pieces look silvery. Breaks into thin, flat flakes -- you can see light through them! Often stuck on or mixed with larger pink, white, and gray crystals. Rounded pebbles If you have a rounded pebble from a beach or river gravel, you may have to go to this page to find its name.Identification of Igneous RocksGrain Usual Other Composition RockSize Color Typefine dark glassy appearance lava glass Obsidianfine light many small bubbles lava froth from sticky lava Pumicefine dark many large bubbles lava froth from fluid lava Scoriafine or light contains quartz high-silica lava Felsite
mixedfine or medium between felsite and medium-silica lava Andesitemixed basaltfine or dark has no quartz low-silica lava Basaltmixedmixed any color large grains in fine- large grains of feldspar, quartz, Porphyry grained matrix pyroxene or olivinecoarse light wide range of color feldspar and quartz with minor Granite and grain size mica, amphibole or pyroxenecoarse light like granite but feldspar with minor mica, Syenite without quartz amphibole or pyroxenecoarse light to little or no alkali plagioclase and quartz with dark Tonalite medium feldspar mineralscoarse medium to little or no quartz low-calcium plagioclase and dark Diorite dark mineralscoarse medium to no quartz; may high-calcium plagioclase and Gabbro dark haveolivine dark mineralscoarse dark dense; always olivine with amphibole and/or Peridotite hasolivine pyroxenecoarse dark dense mostly pyroxene with olivine and Pyroxenite amphibolecoarse green dense at least 90% olivine Dunitevery any color usually in small typically granitic Pegmatitecoarse intrusive bodiesIdentification of Sedimentary RocksHardness Grain Composition Other Rock Type Sizehard coarse clean quartz white to brown Sandstonehard coarse quartz and feldspar usually very coarse Arkosehard or mixed mixed sediment with rock gray or dark and "dirty" Wacke/soft grains and clay Graywackehard or mixed mixed rocks and sediment round rocks in finer Conglomeratesoft sediment matrixhard or mixed mixed rocks and sediment sharp pieces in finer Brecciasoft sediment matrixhard fine very fine sand; no clay feels gritty on teeth Siltstonehard fine chalcedony no fizzing with acid Chert
soft fine clay minerals splits in layers Shale soft fine carbon black; burns with tarry Coal smoke soft fine calcite fizzes with acid Limestone soft coarse or dolomite no fizzing with acid Dolomite fine unless powdered rock soft coarse fossil shells mostly pieces Coquina very soft coarse halite salt taste Rock Salt very soft coarse gypsum white, tan or pink Rock GypsumIdentification of Metamorphic Rocks Foliation Grain Hardness Usual Color Other Rock Type Size foliated fine very soft light greasy feel Soapstone foliated fine soft dark "tink" when struck Slate foliated fine soft dark shiny; crinkly foliation Phyllite foliated coarse hard mixed dark crushed and stretched fabric; Mylonite and light deformed large crystals foliated coarse hard mixed dark wrinkled foliation; often has Schist and light large crystals foliated coarse hard mixed banded Gneiss foliated coarse hard mixed distorted "melted" layers Migmatite foliated coarse hard dark mostly hornblende Amphibolite nonfoliated fine soft greenish shiny, mottled surface Serpentinite nonfoliated fine or hard dark dull and opaque colors, found Hornfels coarse near intrusions nonfoliated coarse hard red and dense; garnet and pyroxene Eclogite green nonfoliated coarse soft light calcite or dolomite by the acid Marble test nonfoliated coarse hard light quartz (no fizzing with acid) Quartzite