Geology and Rocks
Geology is the study of the Earth and what it is made of, including how the Earth is structured, and the changes to the Earth over time. A geologist is a person who studies the Earth, which includes rocks, landslides, earthquakes, volcanoes, and many other elements of the Earth, including its history.
There are three main types of rocks: sedimentary, metamorphic, and igneous.
A sedimentary rock is formed from particles of sand, shells, pebbles, and other pieces of material. All these particles together make up sediment. Sediment is the result of material broken down by weathering or erosion. If you break apart a rock, the small pieces or dust from the rock becomes sediment.
Slowly, sediment accumulates in layers and over a long period of time harden into rock. Sedimentary rock is usually the only type of rock that contains fossils. Fossils are the remains of dead animals or plants usually from long ago. The following are examples of sedimentary rock: limestone, shale, and sandstone
A metamorphic rock is formed under the surface of the earth from the change that takes place due to intense heat or pressure. In nature, it takes millions of years for a metamorphic rock to be formed. The rocks that result from this very long process often have ribbon-like layers and many shiny crystals. The crystals are formed by minerals which grow slowly over time on the surface of the rock. The following are examples of metamorphic rock: marble, slate, and quartzite.
Igneous rocks form when magma cools and hardens. Magma is the molten rock deep within the earth. The same material inside a volcano. Sometimes this magma cools inside the earth. At other times it will erupt onto the surface from a volcano. When magma leaves the volcano, it is called lava.
Lava cools very quickly, crystals do not form, and the rock looks shiny and glasslike. At times, there are gas bubbles trapped inside the rock during the cooling process. If this occurs, there will be tiny holes and spaces left in the rock. The following are examples of igneous rock: basalt, obsidian, and granite.
Rocks and stones are made up of minerals. Minerals are naturally occurring substances formed by geological processes, and many of them are usually solid and feature a crystal structure, plus specific physical properties and chemical composition.
Besides structure, the physical properties of minerals include its hardness, luster or how it reflects light, color, and other properties such as streak, fracture, cleavage, and density. There are over 4,000 different types of minerals including talc, diamonds, calcite, gypsum, gold, quartz, pyrite and others. One of the hardest minerals is diamond and one of the softest is talc.
In summary, geology is the study of the many rocks and minerals found all over the Earth.
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