Amethyst and it can not be differentiated with absolute certainty without advanced gemmological testing (which is often cost-prohibitive). There is one test based on "Brazil law twinning" (a form of quartz twinning where right and left hand quartz structures are combined in a single crystal) which can be used to identify synthetic amethyst rather easily. It is possible to synthesize twinned amethyst, but this type is not available in large quantities in the market. Single-crystal quartz is very desirable in the industry, particularly for keeping the regular vibrations necessary for quartz movements in watches and clocks, which is where a lot
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