Sedimentary rocks are one of the three types of rocks that are composed by the deposition and subsequent cementation of that material at the Earth's surface and in bodies of water. The sediment is compressed over a long period of time before consolidating into solid layers of rock. Examples of sedimentary rocks include limestone, sandstone, mudstone, chalk, coal and flint. Sedimentary rocks forms layers called strata which can often be seen in exposed cliffs.
The Sedimentary Cycle
Examples of some Sedimentary Rocks
Limestone: Limestone is omposed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs. It is found anywhere an ancient ocean used to be.
Siltstone: Siltstone forms where water, wind, or ice deposit silt, and the silt is then compacted and cemented into a rock. It is found in stream deposits, lake beds and most commonly, in Kansas.
Shale: Shale forms from consolidated mud or clay and can be split easily into fragile slabs. It is usually found in areas where gentle waters have deposited sediments that become compacted together.
A metamorphic rock is a result of a transformation of a pre-existing rock. Its name is from ''morph'' (meaning form), and ''meta'' (meaning change). The original rock is subjected to very high heat and pressure. Examples of these rock types include marble, slate, gneiss, schist. Metamorphic rocks make up a large part of the Earth's crust.
The Metamorphic Cycle
Examples of some Metamorphic Rocks
Gneiss: Gneissis a type of metamorphic rock that forms when either a sedimentary or a igneous rock is exposed to intense temperatures and pressure. There are mostly found in New England, the Piedmont, the Adirondacks, and the Rocky Mountains.
Slate: Slate is a fine-grained and foliated metamorphic rock acquired from an original shale-type sedimentary rock that is composed of clay or volcanic ash through low-grade regional metamorphism. It can mainly be found from certain countries such as Brazil and the United Kingdom.
Schist: Schist is a coarse-grained metamorphic rock that has layers of different minerals and can be split into thin irregular plates It can be found in many countries including Brazil, parts of the US and Ireland.
Igneous Rocks are formed through the cooling and solidification of magma or lava. The atoms and molecules of melted minerals are what make up magma. The upper section of the Earth's crust is made up of around 95% igneous rock. There are over 700 different types of igneous rocks but some common examples include basalt, granite, pumice, obsidian, diorite, gabbro and andesite.
The Igneous Cycle
Examples of some Igneous Rocks
Granite: Granite is a very hard igneous rock consisting mainly of quartz, mica, and feldspar and often used as a building stone. They are usually found on continents around the world near active or past plate boundaries.
Diorite: Diorite rocks are usually composed of sodium-rich plagioclase with smaller amounts of hornblende and biotite. It is produced in volcanic arcs, and in by mountain buildings.
Gabbro: Gabbro rocks refer to a large group of dark, coarse-grained, mafic intrusive igneous rocks. It forms when molten magma is trapped beneath the Earth's surface and slowly cools into a holocrystalline mass.
Tools that test hardness in rocks
A fingernail has hardness of 2.5. A copper penny has hardness of about 3.5. A knife blade has a hardness of 5.5. Window glass and steel file have a hardness of 6.5. These following items help show how the items are affected by the hardness of the rock.