Rock

Sedimentary

Description

Limestone
Limestone: The specimen shown is about two inches (five centimeters) across.

Breccia
Chert Breccia: The angular clasts in this breccia are chert fragments. The matrix is an iron-stained mix of clay through sand-si

Chert
Chert: This specimen of chert is about two inches (five centimeters) across. It displays conchoidal fracture and has broken to

Phyllite
Phyllite: The specimen shown is about two inches (five centimeters) across.

Coal
Bituminous Coal: Bituminous coal is typically a banded sedimentary rock. In this photo you can see bright and dull bands of c

Igneous rocks

Pegmatite


Pegmatite is a light-colored, extremely coarse-grained intrusive igneous rock. It forms near the margins of a magma chamber

Andesti

Andesite is a fine-grained, extrusive igneous rock composed mainly of plagioclase with other minerals such as hornblende, pyro

Basalt

Basalt is a fine-grained, dark-colored extrusive igneous rock composed mainly of plagioclase and pyroxene. The specimen shown i

Peridotite

Peridotite is a coarse-grained intrusive igneous rock that is composed almost entirely of olivine. It may contain small amoun

Diorite

Diorite is a coarse-grained, intrusive igneous rock that contains a mixture of feldspar, pyroxene, hornblende and sometimes quar

Metamorphic rocks


Phyllite

is a foliate metamorphic rock that is made up mainly of very fine-grained mica. The surface of phyllite is typically lustrous and sometimes wrinkled. It is intermediate in grade between slate and schist. The specimen shown above is about two inches (five centimeters) across.


Amphibolite

is a non-foliated metamorphic rock that forms through recrystallization under conditions of high viscosity and directed pressure. It is composed primarily of amphibole and plagioclase, usually with very little quartz. The specimen shown above is about two inches (five centimeters) across.

Gneiss

is foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains. It typically contains abundant quartz or feldspar minerals. The specimen shown above is about two inches (five centimeters) across.


Quartzite

is a non-foliated metamorphic rock that is produced by the metamorphism of sandstone. It is composed primarily of quartz. The specimen above is about two inches (five centimeters) across.


Hornfels

is a fine-grained nonfoliated metamorphic rock with no specific composition. It is produced by contact metamorphism. Hornfels is a rock that was "baked" while near a heat source such as a magma chamber, sill or dike. The specimen shown above is about two inches (five centimeters) across.