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How are gemstones formed?

Various conditions in the Earth lead to the formation of minerals. Most gemstones will be formed on the top layer of the earth, also known as the crust, which has a varying depth of about 3 to 25 miles. There are only two types of gemstones which are formed in the mantle of the earth, and these are the Peridot and the diamond; the mantle forms about 60 percent of the total volume of the earth. It is known that the mantle has a molten rocky mass, called magma, and this has a solid upper layer.

Although few gemstones are formed in the mantle, all of the gemstones that you find in the market today are mined from the crust. There are three types of rocks forming the crust, and these are the metamorphic, sedimentary and igneous rocks. These are terms which tell you how the rocks were formed. Most gemstones are associated with one specific type of rock even if there are others which are associated with the other forms.

Igneous rocks are formed through the cooling and solidification of molten magma. Magma will find its way to the top of the crust, usually through fissures in the overlying rocks called volcanic pipes. When it reaches to the surface, it is now called lava, and this usually solidifies when it cools down. However, if the solidification process is slow, usually within the crust, then there is the possibility if the formation of minerals, through crystallization. If there is an increase in the pressure then the molten lava can also be pushed into the surrounding rocks and there is some chemical exchange. There is a very long list of gemstones which are associated with the formation of igneous rocks. All quartz types, such as ametrine, amethyst and citrine are associated with these rocks. Others are the Chrysoberyl group, garnet, moonstone, spinel, zircon, topaz, tourmaline, apatite, diamond and beryl, such as aquamarine, Morganite and emerald.

Upon reaching the surface if the earth, the igneous rock is subjected to the forces of weathering and erosion, and you get smaller particles being formed from these rocks, from where they are moved by water and wind, or simply accumulate at the surface. Over the years, the layers of these sediments are piled up on one another and hidden in the crust, or under water masses. It is the pressure from the overlaying layers, upon those beneath that causes them to go through various chemical and physical changes, such as lithification, and these lead to the formation of sedimentary rock. Evaporation in conjunction with other processes can also lead to the formation of sedimentary rocks; a great example are the rocks which are found in deserts. The gemstones which are formed through this process include opal, zircon, malachite and jasper.

Contact metamorphism is the process in which intrusive magma enters into a certain rock formation. Regional metamorphism is that which is brought about through the motions of large tectonic plates of the earth’s crust. Regional metamorphism puts a lot of pressure on sedimentary and igneous rocks, making the minerals to heat up and given the pressure they undergo certain physical and chemical changes, which leads to the formation of metamorphic rocks. The gemstones that are associated with the metamorphic process include sapphire, beryl, lapis lazuli, spinel, turquoise and jade.

The rock cycle is a process that is used to describe the way that rocks and minerals are constantly changing. It is possible to get metamorphic rocks forming from sedimentary or igneous rocks. Sedimentary rocks can also change into igneous or metamorphic rocks. You can also get igneous rocks form metamorphic or sedimentary rocks; and the process continues for centuries so patience is necessary.



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