digital rock collection

IGNEOUS ROCKS

BASALT

• Basalt is a dark-colored,igneous rock composed mainly of plagioclase and pyroxene minerals.
• It most commonly forms as an extrusive rock, such as a lava flow, but can also form in small intrusive bodies, such as an igneous dike or a thin sill.

GABBRO

• Gabbro is a coarse-grained, dark-colored, intrusive igneous rock.
• It is usually black or dark green in color and composed mainly of the minerals plagioclase and augite.

PUMICE

• Pumice is a light-colored, extremely porous igneous rock that forms during explosive volcanic eruptions.
• It is used as aggregate in lightweight concrete, as landscaping aggregate, and as an abrasive in a variety of industrial and consumer products.

OBSIDIAN

• Obsidian is an igneous rock that forms when molten rock material cools so rapidly that atoms are unable to arrange themselves into a crystalline structure.
• It is an amorphous material known as a "mineraloid."

SEDIMENTARY ROCKS

CONGLOMERATE

• Conglomerate is a clastic sedimentary rock that contains large (greater then two millimeters in diameter) rounded particles. The space between the pebbles is generally filled with smaller particles and/or a chemical cement that binds the rock together. The specimen shown above is about two inches (five centimeters) across.

LIMESTONE

• Limestone is a rock that is composed primarily of calcium carbonate. It can form organically from the accumulation of shell, coral, algal and fecal debris. It can also form chemically from the precipitation of calcium carbonate from lake or ocean water. Limestone is used in many ways. Some of the most common are: production of cement,

SANDSTONE

• Sandstone is a clastic sedimentary rock made up mainly of sand-size (1/16 to 2 millimeter diameter) weathering debris. Environments where large amounts of sand can accumulate include beaches, deserts, flood plains and deltas. The specimen shown above is about two inches (five centimeters) across.

SHALE

• Shale is a clastic sedimentary rock that is made up of clay-size (less then 1/256 millimeter in diameter) weathering debris. It typically breaks into thin flat pieces. The specimen shown above is about two inches (five centimeters) across.

metamorphic rocks

SCHIST

• Shale is metamorphic rock with well developed foliation. It often contains significant amounts of mica which allow the rock to split into thin pieces. It is a rock of intermediate metamorphic grade between phyllite and gneiss.

SLATE

• Slate is a fine-grained, foliated metamorphic rock that is created by the alteration of shale or mudstone by low-grade regional metamorphism. It is popular for a wide variety of uses such as roofing, flooring and flagging because of its durability and attractive appearance.

MARBLE

• Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone or dolostone.

QUARTZITE

• Quartz is a chemical compound consisting of one part silicon and two parts oxygen. It is silicon dioxide (SiO2). It is the most abundant mineral found at Earth's surface and its unique properties make it one of the most useful natural substances.

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