Igneous, Sedimentary, and Metamorphic Rocks: Key Characteristics and Identification

Obsidian Igneous rock

black, glassy texture

Rhyolite Igneous rock

felsic like granite, small crystals (extrusive)

Diorite Igneous rock

"cookies and cream" appearance

Gabbro Igneous rock

dark color, big crystals

Scoria Igneous rock

dark red color, large holes, lightweight

Basalt Igneous rock

mafic like gabbro, dark color, small crystals

Pumice Igneous rock

very holey, lightweight, light color

Granite Igneous rock

countertop material, big crystals

Rock Salt Sedimentary rock

pink-ish, looks like salt

Chert Sedimentary rock

very hard to scratch, grayish color

Chemical Limestone Sedimentary rock

smooth feel, reacts to acid, soft

Fossil Limestone Sedimentary rock

fizzes with acid, contains small shell pieces

Coal Sedimentary rock

Conglomerate Sedimentary rock

rounded fragments

Breccia Sedimentary rock

irregular (angular) fragments

Chalk Sedimentary rock

microscopic shell fragments, reacts to acid

Coquina Sedimentary rock

large shell pieces cemented together

Shale Sedimentary rock

made of clay, smoothest clastic rock

Siltstone Sedimentary rock

larger grains than shale, slightly rough (don't use color)

Sandstone Sedimentary rock

looks like sand stuck together, rough feel

Gneiss Metamorphic rock

visible layers (foliation)

Schist Metamorphic rock

shiny, fish-scale look, light & dark minerals

Marble Metamorphic rock

white, fizzes when exposed to acid

Soapstone Metamorphic rock

very soft, greasy feel

Quartzite Metamorphic rock

off-white or pink, very hard

Hornfels Metamorphic rock

usually black, slight banding

Slate Metamorphic rock

black, breaks into sheets

Phyllite Metamorphic rock

shiny gray color