Igneous - formed from molten (liquid) rock.

A. Intrusive (Plutonic) - formed from magma

(1) Granite - bedrock for the continents; you can see the crystals
(2) Pegmatite - very large crystals

B. Extrusive (Volcanic) - formed from lava
(1) Basalt - makes up the ocean floor
(2) Obsidian - black and glassy - arrowheads
(3) Pumice - lighter than water - floats
(4) Scoria - feather rock - many gas pockets

Sedimentary - usually layered

A. Clastic - formed from pieces of other rocks
(1) Conglomerate - rounded pebbles cemented together
(2) Breccia - like conglomerated - but angular
(3) Sandstone - sand sized grains
(4) Shale - very fine grains - mud sized particles

B. Chemical - formed from dissolved minerals
(1) Limestone - reacts with hydrochloric acid
(2) Rock salt - water evaporates leaving salt

C. Organic - formed from once living things
(1) Coquina - shells cemented together
(2) Coral reefs - sea life
(3) Coal - plants that died millions of years ago

Metamorphic - formed from existing rocks by heat and pressure

(1) Gneiss - pronounced nice - minerals arranged in parallel bands
(2) Shist - visible layers of flaky minerals
(3) Marble - changed limestone
(4) Slate - chjanged shale