Rocks and Landforms

                                                             By: Madason Hayes

Sedimentary Rocks

Description: Sedimentary rocks are formed by the accumulation of sediments.

Sandstone: Sandstone is a sedimentary rock composed of sand-sized grains of mineral, rock or organic material. It also contains a cementing material that binds the sand grains together and may contain a matrix of silt- or clay-size particles that occupy the spaces between the sand grains. Sandstones are also one of the most common sedimentary rocks found in sedimentary basin.

Shale: Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite.

Breccia: is a rockcomposed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments.

Limestone: It most commonly forms in clear, warm, shallow marine waters. It is usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal and fecal debris. It can also be a chemical sedimentary rock formed by the precipitation of calcium carbonate from lake or ocean water.


Igneous Rocks

Description: Igneous rocks are formed from the solidification of molten rock material.

Pegmatite: Pegmatites are extreme igneous that form during the final stage of a magma’s crystallization. They are extreme because they contain exceptionally large crystals and they sometimes contain minerals that are rarely found in other types of rocks.

Pumice: Pumice is a powdered or dust form, is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. It is typically light colored.

Obsidian: Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. It forms when molten rock material cools so rapidly that atoms are unable to arrange themselves into a crystalline structure.

Scoria: Scoria is a dark-colored igneous rock with abundant round bubble-like cavities known as vesicles. It ranges in color from black or dark gray to deep reddish brown. Scoria usually has a composition similar to basalt, but can also have a composition similar to andesite. Many people believe that small pieces of scoria look like the ash produced in a coal furnace. That has resulted in particles of scoria being called "cinders" and the small volcanoes that erupt scoria to be called "cinder cones".

Peridotite: Peridotites usually contain olivine as their primary mineral, frequently with other mafic minerals such as pyroxenes and amphiboles. Their silica content is low compared to other igneous rocks, and they contain very little quartz and feldspar.

Metamorphic Rocks

Description: Metamorphic rocks have been modified by heat, pressure and chemical process usually while buried deep below Earth's surface.

Phyllite: 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.

Soapstone: Soapstone is a metamorphic rocks, that is composed primarily of talc, with varying amounts of chlorite, jmicas, amphiboles, carbonates and other minerals.

Gneiss: 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.

Quartzite: Quartzite is a non-foliated metamorphic rock that is produced by the metamorphism of sandstone. It is composed primarily of quartz.

Marble: Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism. It is composed primarily of the mineral calcite and usually contains other minerals such as clay minerals, micas, quartz, pyrite, iron oxides and graphite.