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 (F116) took place in the North Atlantic, south of Waterford and resulted in the loss of all 49 of the U-boat's crew. During the war the "Amethyst" was credited, along with the sloops , , , and frigate , with sinking the in the North Channel on 16 January 1945. The British Admiralty withdrew this credit in a post-war reassessment. On 20 April 1949, "Amethyst" was on her way from Shanghai to Nanking (now Nanjing) when she was fired upon by the People's Liberation Army, thus starting the Amethyst Incident. "Amethyst" was trapped in China until 30 July 1949 when she