Provides a primary presentation of the basic rock types. Includes five each of igneous, sedimentary and metamorphic rocks, totaling 15 specimens, approximately 1 1/2" x 1 1/2".

INTRODUCTORY ROCK COLLECTION
This rock collection contains fifteen rocks that are representative of the three major rock types: Igneous, Sedimentary and Metamorphic.

IGNEOUS ROCKS are formed by the cooling of molten rock, either magma or lava.

1. OBSIDIAN is a black or brown volcanic rock composed of quartz and alkali feldspar.
2. GRANITE is a medium to coarse-grained rock derived from magma and is composed primarily of the minerals quartz and alkali feldspar.
3. BASALT is a microcrystalline dark colored lava rock composed mainly of calcic plagioclase and clinopyroxene.
4. SCORIA is a dark colored, vesicular, crust on the surface of lava. The vesicles are the result of escaping gas before solidification.
5. RHYOLITE is a usually light colored lava rock that is of the same composition as granite.

SEDIMENTARY ROCKS are rocks derived from preexisting rocks through the processes of erosion, followed by compaction, or chemical precipitation.

6. SHALE is a rock composed of clay, silt, or mud sized particles that is typically fissile.
7. BRECCIA is composed of angular fragments of limestone or quartz formed by friction or crushing processes.
8. SANDSTONE is essentially sand-sized particles cemented together by calcite, silica, or iron oxides.
9. CONGLOMERATE is a coarse-grained rock composed of rounded fragments set in a fine-grained matrix of sand or silt or other cementing materials.
10. LIMESTONE is a generally light colored rock composed mainly of calcium carbonate formed by either organic or inorganic processes.

METAMORPHIC ROCKS are rocks that are recrystallized by pressure and heat that may or may not be influenced by the introduction of chemically active solutions.

11. SLATE is metamorphosed shale and can be broken along planes independent of original bedding planes.
12. MARBLE is recrystallized limestone (calcite).
13. QUARTZITE is a recrystallized sandstone or chert consisting mainly of quartz.
14. GNEISS is a metamorphosed rock that exhibits alternate banding of granular mineral and flaky minerals.
15. SCHIST is a metamorphosed shale or siltstone composed of parallel aligned micas, amphiboles, pyroxenes or garnets.