Crystals of the mineral Pyrite from Peru
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Courtesy of Corel
Type of Minerals
So far, over 2000 minerals have been found, and every year new ones are discovered. This is a pretty overwhelming number of different types of minerals, however, you don't need to know them all to be a rock hound. In fact, only a few dozen are common within the rocks of the Earth's crust so it is only a limited number of minerals that you are likely to find in your backyard.
Minerals are divided into different groups based on their chemical components.
The most common mineral group on Earth is the silicate minerals, which all have the elements silica and oxygen as their primary components. Most silicate minerals form when molten rock cools. Molten rock at or near the Earth's surface cools very quickly and crystals stay very small because they don't have time to grow large. Molten rock that is deep underground, where temperatures and pressures are very high, will cool slowly allowing time for large crystals to grow.
There are many different groups of other minerals that are known as non-silicate minerals. Some of these groups form when magma cools, while others form when water evaporates away, or when other minerals decompose.
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