How Do We Classify Rocks

How Do We Classify Rocks? *

Rocks can be classified into three major families.

Kind of Rock

How Formed

Location

Interesting Stuff

sedimentary

limestone, sandstone, chalk, coal, rock salt, shale, dolomite

formed when many layers of sediment (mud, sand, gravel, and minerals) settle to the bottom of the ocean and are then compacted (pressed together) over thousands of years.

usually in places where oceans or bodies of water did or still exist

soft, layered, may contain fossils

igneous

quartz, pumice, granite, basalt, obsidian

created when molten rock (lava) inside the earth pushes up through the crust. Some types form and cool deep within the earth and are exposed by weathering.

in areas where volcanoes exist

glossy or shiny, usually course-grained

metamorphic

marble, slate, gneiss, schist, quartzite

created when sedimentary or igneous rocks change as a result of high pressure and heat acting on the rocks.

deep within the earth (where pressure and heat have a very large effect)

hard, may contain bands or layers, often contain crystals

* courtesy of http://members.home.net/kostek/kostek/rockscla.htm

Kind of Rock	How Formed	Location	Interesting Stuff
sedimentary limestone, sandstone, chalk, coal, rock salt, shale, dolomite	formed when many layers of sediment (mud, sand, gravel, and minerals) settle to the bottom of the ocean and are then compacted (pressed together) over thousands of years.	usually in places where oceans or bodies of water did or still exist	soft, layered, may contain fossils
igneous quartz, pumice, granite, basalt, obsidian	created when molten rock (lava) inside the earth pushes up through the crust. Some types form and cool deep within the earth and are exposed by weathering.	in areas where volcanoes exist	glossy or shiny, usually course-grained
metamorphic marble, slate, gneiss, schist, quartzite	created when sedimentary or igneous rocks change as a result of high pressure and heat acting on the rocks.	deep within the earth (where pressure and heat have a very large effect)	hard, may contain bands or layers, often contain crystals