Corundum is an allochromatic mineral, meaning that it is colourless in its pure state. Its colour is due to the presence of impurities and atoms of different natures, or to defects in the crystal lattice. Corundum is made up of aluminium oxide crystals formed in the deep lithosphere at very high pressures and temperatures. They were then transported to the surface by magma from the Earth's mantle. The presence of trace elements in varying proportions, which replace the aluminium in the corundum, gives sapphire its colour. These chromogenic elements are mainly iron, titanium and, to a lesser extent, chromium, which could indicate that blue, yellow and green sapphires are formed at a lower depth than rubies. Iron and titanium are found in greater quantities at the surface of the earth's crust, and chromium and vanadium at greater depths. [block id="best-products-sapphire"]

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