Different types of gemstones are formed under varying levels of pressure and temperature. Hence it should come as no surprise that many types of gemstones are formed in volcanic regions or dormant regions. This is due to the fact that a volcanic eruption throws out a lot of minerals and other trace elements. Rare gemstones that have formed deep inside earth over the years are sometimes brought to the surface through a volcanic eruption. Other places that abound with gemstones are those areas that have undergone metamorphosis over many years.
The following paragraphs contain data explaining the process of the formation of gemstones. This data will also help you identify places where gemstones can be found.
Gemstones formed due to the crystallization of magma
The tremendous pressure inside the earth squeezes out magma which cools into lava. During this process several types of gemstone are formed. Some of these are topaz, corundum stones and the moonstone. Diamonds are formed at great depths under great pressure. They are forced up with magma. Or they may be formed in the earth’s mantle when magma is forced upwards and cools.
Gemstones formed due to Pegmatite formation
Pegmatite is a type of igneous rock formed as magma cools and solidifies into large crystals. The liquid that remains during the cooling process contains a high amount of silica. This liquid gets squeezed into crevices and cracks in the surrounding rocks due to pressure and gravity. It reacts with a variety of minerals present in the rocks to form gemstones. The gems formed in this way are – quartz, topaz, beryl, spodumene and tourmaline.
Gemstones formed in hydrothermal veins
After a large part of the silicate liquid has been used in reactions, the remaining water contains a large number of chemicals. This is called hydrothermal liquid and the rock fissures in which this liquid fills are called hydrothermal veins. As this liquid fills up different types of fissures in the rocks, the chemicals present in this liquid react with the minerals present in the rock. This leads to the formation of gemstones like benitoite, emerald, beryl (mostly red beryl) and topaz.
Gemstones formed due to chemical precipitates
The liquid that gets trapped in volcanic rock gets filtered as it passes down through porous volcanic rocks. Such rocks contain a good amount of phosphorous and aluminium. Highly acidic copper that remains in the liquid reacts with these minerals to form turquoise. Other gemstones that are formed in a similar manner are opal, malachite and rhodochrosite.
Gemstones formed in alluvial deposits
Alluvial deposits are found in streams and river beds. These are remnants of rocks that have ruptured and disintegrated. The remains of this disintegration process are hardened minerals that are resistant to weathering. They are washed down streams and rivers after rains and precipitate at river bottoms. Over time the external pressure transforms them into gemstones like ruby, zircon, sapphire, quartz, garnet, diamond and chrysoberly. Large deposits of rubies have been formed by this process in Sri Lanka, Burma and in India.
Gemstones formed in metamorphic deposits
Over millions of years, rocks embedded in soil experience rising temperature and pressure. This alters the chemical composition of the rocks to such an extent that it forms new types of minerals. Some of these minerals are used as gemstones. Gems formed through this process are corundum, garnet, epidote, diopside, kyanite, andalusite and silimanite.
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