How do you identify what sort of rock you found?

Answer 1

Of course, since we can't see a picture of your rock, we can't be certain, but here's how you can identify your own rock:

What size are the minerals making up the rock?

• Can't see individual grains and rock is thin and heavy - probably a shale, which is a metamorphic rock made from sandstone that has been squeezed under pressure for millions of years
• Can't see individual grains and rock is brittle and breaks in sheets - probably a sedimentary rock called slate, made of mud packed together over millions of years
• Can't see individual grains and rock looks like a piece of glass - obsidian, which is a volcanic type of glass formed from melting sand
• Can't see individual grains and rock looks like clay - probably limestone if it's a softer rock or chert if it's a harder rock
• Very small grains and rock is very hard and usually white or light colored - probably a metamorphic rock called quartzite
• Very small grains and rock is fairly soft and usually white or light colored - probably a metamorphic rock called marble
• Very small grains like sand or mud - an igneous rock called sandstone or siltstone
• Very small grains but doesn't look like clay or mud - an igneous or volcanic type of rock called rhyolite (light color) or andesite (medium color) or basalt (dark color)
• Medium grains - probably an igneous rock called dacite (medium color) or diabase (dark color)
• Medium grains and looks sort of like concrete with minerals and sandstone pieces in it - a sedimentary rock called graywacke
• Medium grains with a definite order to the crystals inside the rock - a metamorphic rock called schist
• Medium grains with definite layers of dark and light minerals - a metamorphic rock called gneiss
• Coarse grains with rounded pieces - a sedimentary rock called a conglomerate
• Coarse grains with jagged pieces - a sedimentary rock called breccia
• Coarse grains with no real order to the minerals in the rock - an igneous rock called granite (light color) or diorite (medium color) or gabbro (dark color) or peridotite (very dark color)
• Frothy looking with bubbles - an igneous rock called pumice (light color) or scoria (dark color)
• Made of tiny fossils - a sedimentary rock called coquina
• Alternating layers of light colored igneous rock and dark colored gneiss, usually highly folded and contorted - a metamorphic rock called migmatite

Of course, you may have found a piece of a mineral, not a rock at all. Your best bet is to start looking on the internet for photos that look like what you found. Here are a couple of good places to start:

• Geology.com - photos of different types of rocks with identifications
• Rock Picture Index - click on the different names to see what the rock looks like