In most cases, they formed at depths of 6–18 miles in the earth’s crust, as intense pressures and high temperatures above 800 degrees transformed sedimentary (“water deposited”) rocks, such as siltstones and shale. Some Sapphire gemstones are found in high-grade metamorphic rocks and in igneous rocks, called gneisses and granulites, located in Australia, Sri Lanka, India, Madagascar, and Eastern Africa. At some point, millions of years ago, source rocks inside the earth’s crust were subjected to intense pressures and high temperatures, causing the atoms to recombine into new metamorphic (changed) rocks which included rubies and sapphires (corundum). The answer as to what took place inside the earth to form these gems and then transport them to the surface varies from country to country, but the story remains the same. The main deposits of high-quality sapphire gemstones are found only in a few places, mainly in southern Asia and eastern Africa and the islands of Sri Lanka (Ceylon) and Madagascar. Thus, all colours of the translucent form of the mineral corundum are known as sapphires. This star-shaped effect is known as an asterism and is a less pure form of sapphire. Some more interesting varieties of sapphire with rutile (the ore form of titanium) intrusions cause light to be reflected in a six-point star, creating what is known as a star sapphire. The natural crystal form of sapphire is called a trigonal (three-sided prisms). Sapphires also come in orange-pink, golden, white, and even black. These are the blue gemstones most often seen in jewellery, with colours ranging from pale, ice blue to deep, cobalt blue, but did you know that sapphires also come in other colours?īlue is just the more highly prized variant of the mineral corundum. The word Sapphire comes from the Greek “Sapphires”, which means blue.
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