Amethyst even if the iron concentration is low. Natural amethyst is dichroic in reddish violet and bluish violet, but when heated, turns yellow-orange, yellow-brown, or dark brownish and may resemble citrine, but loses its dichroism, unlike genuine citrine. When partially heated, amethyst can result in ametrine. Amethyst can fade in tone if overexposed to light sources and can be artificially darkened with adequate irradiation. Amethyst was used as a gemstone by the ancient Egyptians and was largely employed in antiquity for intaglio engraved gems. The largest Ancient Egyptian amethyst mines are located at Wadi el-Hudi and those mines may be the
HMS Amethyst (1799) Frigate, at the Action of 6 April 1809. "Niémen" had 47 killed and 73 wounded; "Amethyst" had eight killed and 37 wounded. In 1847 the Admiralty authorized the issue of the Naval General Service Medal with clasp "Amethyst 5 April 1809". Later in the year, Seymour participated in the Walcheren Expedition, providing naval support to the transports. On 11 August she was part of a squadron under Captain William Stewart that forced the passage between shore batteries at Flushing and Cadsand. "Amethyst" had one man killed and one man wounded in the operation. Seymour left the ship in 1809; his