• Extrusive• Intrusive

Granite is a coarse-grained, light colored, intrusive igneous rock that contains mainly quartz and feldspar minerals.

Rhyolite is a light-colored, fine-grained, extrusive igneous rock that typically contains quartz and feldspar minerals.

Gabbro is a coarse-grained, dark colored, intrusive igneous rock that contains feldspar, augite and sometimes olivine.

Basalt is a dark-colored, fine-grained, 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. It has a composition similar to gabbro. The difference between basalt and gabbro is that basalt is a fine-grained rock while gabbro is a coarse-grained rock.

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

Andesite is a fine-grained, extrusive igneous rock composed mainly of plagioclase with other minerals such as hornblende, pyroxene and biotite. The specimen shown is about two inches (five centimeters) across.

Obsidian is a dark-colored volcanic glass that forms from the very rapid cooling of molten rock material. It cools so rapidly that crystals do not form.

Pumice is a light-colored vesicular igneous rock. It forms through very rapid solidification of a melt. The vesicular texture is a result of gas trapped in the melt at the time of solidification.

Scoria is a dark-colored, vesicular, extrusive igneous rock. The vesicles are a result of trapped gas within the melt at the time of solidification. It often forms as a frothy crust on the top of a lava flow or as material ejected from a volcanic vent and solidifying while airborne.

• Clastic• Nonclastic

Breccia is a term most often used for clastic sedimentary rocks that are composed of large angular fragments (over two millimeters in diameter). The spaces between the large angular fragments can be filled with a matrix of smaller particles or a mineral cement that binds the rock together.

Conglomerate could be thought of as a giant sandstone, containing grains of pebble size (greater than 4 mm) and cobble size (>64 mm).

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.

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.

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. Some of the most common uses are: production of cement, crushed stone and acid neutralization.

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. Some of the most common uses are: production of cement, crushed stone and acid neutralization.

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.

Coal is an organic sedimentary rock that forms from the accumulation and preservation of plant materials, usually in a swamp environment. Coal is a combustible rock and along with oil and natural gas it is one of the three most important fossil fuels. Coal has a wide range of uses; the most important use is for the generation of electricity.

Rock salt is an evaporite like rock gypsum, composed of the mineral halite, which is the same as table salt.

Chert is a microcrystalline or cryptocrystalline sedimentary rock material composed of silicon dioxide (SiO2). It occurs as nodules, concretionary masses and as layered deposits. Chert breaks with a conchoidal fracture, often producing very sharp edges. Early people took advantage of how chert breaks and used it to fashion cutting tools and weapons. Dark varieties of chert are common and are often called "flint“.

Breccia is a term most often used for clastic sedimentary rocks that are composed of large angular fragments (over two millimeters in diameter). The spaces between the large angular fragments can be filled with a matrix of smaller particles or a mineral cement that binds the rock together.

Conglomerate could be thought of as a giant sandstone, containing grains of pebble size (greater than 4 mm) and cobble size (>64 mm).

Foliated

Nonfoliated

Slate is a foliated metamorphic rock that is formed through the metamorphism of shale. It is a low grade metamorphic rock that splits into thin pieces.

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.

Schist is formed by regional metamorphism and has schistose fabric—it has coarse mineral grains and is fissile, splitting in thin layers.

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.

• from limestone• composed primarily of calcium carbonate.

• sandstone• primarily of quartz

DioriteAndesite

Figure 4.7 B