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
Amethyst Mountain exposures of well known and visited petrified forests. The summit of Amethyst Mountain is traversed by Specimen Ridge Trail, which also traverses the south side of Specimen Ridge between Tower Junction and Soda Butte Creek and through the Yellowstone Petrified Forest. Amethyst Mountain consists of a geological formation known as the Lamar River Formation. Within the Amethyst Mountain area, it is over thick and consists predominantly of conglomerate and lesser proportions of tuffaceous sandstone and siltstone. Volcanic breccia is absent and only a very few thin airfall volcanic ash beds have been identified in the exposures at Amethyst Mountain. The