White Marble Mostly bright white Made of medium-sized crystals that glitter in sunlight. You can scratch it with a nail or knife.scratch it with a nail Dolostone Mostly light gray Made mostly of small-sized crystals that may or may not glitter in sunlight. You can scratch it with a nail or knife.scratch it with a nail White Chert Mostly white, sometimes chalky looking or smooth Broken edges may be scalloped or sharp. Nail doesn't scratch it (but may leave a dark line).scratch it White or light gray

Quartzite pebbles White (also yellowish or light brown) Can see large sand grains -- sometimes crumbly. Nail doesn't scratch it (but may leave a dark line).scratch it

Slate Dark gray, looks silky in the sun. Breaks into mostly flat pieces. ScoriaScoria (type of Basalt) Black or reddish. Lots of rounded bubble holes. Doesn't float in water. Coal Black Either smooth and shiny, or dull and crumbly Draws a black line if you scrape it on the sidewalk. Dark gray or black

ScoriaScoria (a type of Basalt) Reddish or black Lots of bubble holes Doesn't float in water. Pink Quartzite Pink If you look closely, you may see some pieces are made of sand-sized grains. Quartz rock Most pieces stained rusty red or yellowish, or coated with rusty-red powder. If you look closely, you'll see small, pointy crystals and thinly layered rock. Red or pink or rusty looking

Brown Chert Mostly brown, but mixed with cream and darker colors. Some sides look really smooth, but freshly broken edges may be sharp! Nail doesn't scratch it (but may leave a dark line).scratch it Quartzite pebbles Brownish, yellowish, or white Can see large sand grains in some pieces -- sometimes crumbly. Nail doesn't scratch it (but may leave a dark line).scratch it Brown QuartziteBrown Quartzite pebbles Brownish, tan, white, or reddish Outside very rounded and smooth Broken edges look glassy and may be sharp. Nail doesn't scratch it (but may leave a dark line).scratch it

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.scratch it with a nailbubbles in vinegar or acid White Chert Mostly white, sometimes chalky looking or smooth. Broken edges may be sharp or scalloped. Nail doesn't scratch it and it does not bubble in vinegar.scratch itdoes not bubble in vinegar White or light gray

White Granite Mostly white or yellowish, with dark specks. Small broken crystal surfaces shine in sunlight. Nail doesn't scratch it and it does not bubble in vinegar.scratch itdoes not bubble in vinegar Dolostone Mostly light gray. You can scratch it with a nail or knife.scratch it with a nail Only powdered rock bubbles in vinegarOnly powdered rock bubbles in vinegar or acid.

Limestone Light to dark gray. You can scratch it with a nail or knife.scratch it with a nail Rock bubbles in vinegar or acid.bubbles in vinegar 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.bubble in vinegar

QuartzQuartz (from Pegmatite)Pegmatite Cloudy white, a bit pinkish, or clear. Looks a bit like broken glass. Nail doesn't scratch it and it does not bubble in vinegar or acid.scratch itdoes not bubble in vinegar Quartzite pebbles White (also yellowish or light brown). Can see large sand grains -- sometimes crumbly. Nail doesn't scratch it and it does not bubble in vinegar or acid.scratch itdoes not bubble in vinegar

Slate Dark gray, looks silky in the sun. Breaks into mostly flat pieces. BasaltBasalt or "Trap Rock" Dark gray, dull looking. Mostly fine-grained, but may contain scattered larger crystals. Breaks into chunks with smooth sides. ScoriaScoria (type of Basalt) Black or reddish. Lots of rounded bubble holes. Doesn't float in water. Dark gray or black

SlagSlag (human-made lava) Black, whitish, or reddish. Some rounded bubble holes, but mixed with crumbly places and smooth glassy spots. Some parts fizz in acid. ObsidianObsidian 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!

Coal Draws 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.

ScoriaScoria (a type of Basalt) Reddish or black. Lots of bubble holes. Doesn't 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, you'll also see gray and purplish spots. Red or pink or rusty looking

SaproliteSaprolite ("weathered" granite) Most pieces stained rusty red or coated with a dark reddish crust. If you look closely, you'll see pink, gray, and darker crystals (like in Red Granite). PegmatitePegmatite (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, you'll see small, pointy crystals and thinly layered rock.

Brown Chert Mostly brown, but mixed with cream and darker colors. Some sides look really smooth, but freshly broken edges may be sharp! Nail doesn't scratch it (but may leave a dark line).scratch it Pumice Tan or gray. Lots of bubble holes. Feels very light in weight, for a rock. Dry pieces often float in water. Brown, tan, or yellowish

Quartzite pebbles Brownish, yellowish, or white. Can see large sand grains in some pieces -- sometimes crumbly. Nail doesn't scratch it (but may leave a dark line).scratch it Brown QuartziteBrown Quartzite pebbles Brownish, tan, white, or reddish. Outside very rounded and smooth. Broken edges look glassy and may be sharp. Nail doesn't scratch it (but may leave a dark line).scratch it

MicaMica (in Pegmatite)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. Silvery