Until the 18th century, amethyst quartz was one of the central precious stones, and it was even known as the Queen of Precious Stones, being at the same level as the diamond.
With the discovery of gem deposits in Brazil, its price has gone down, making it an affordable gemstone.

The colour of amethyst is due to the presence of iron (Fe2 +) and aluminium (Al) in its composition, but when heated or subjected to ultraviolet radiation, it can become almost colourless.
When exposed to temperatures of around 500 ºC, amethyst quartz becomes yellowish, a "variety" known as "burnt amethyst".
This change in colour is the result of an oxidation process, that is, Fe2 + becomes Fe3 +. Amethyst quartz exposed to sunlight easily indeed loses its colour.

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