12/7/2023 0 Comments Red purple gems and crystals![]() ![]() Port Arthur was the name of a port in the Kwantung Province of Manchuria this area was an historic producer of very fine amethyst. The latter have been called Port Arthur Amethyst. Most of the amethyst from Thunder Bay is strongly color zoned and these zonations appear as chevrons if the cut is diagonal to the c-axis of the crystal or sometimes as six triangles of alternating purple and colorless or white areas if the cut is made perpendicular to the c-axis of the crystal. The status of the mines and fee localities varies from year to year so it is best for one to write or call ahead before planning trips to these areas. There are several commercial mines and several fee localities where one can pay to collect. In North America a great deal of amethyst is extracted from mines in the Thunder Bay, Ontario, Canada, area. Some of the Mexico specimens had nice small phantom crystals of amethyst in a colorless body of rock crystal. When I first took up lapidary in 1961, there were some amethyst tips from Mexico that were nicely colored and produced fine cabochons but they were all nearly opaque. The amethyst from Mexico has produced many fine, large cabinet specimens that appear in both private and museum collections. Some very attractive amethyst has been produced in Mexico but most of it that has been of desirable gem shades formed in crystals that were quite small and many of the larger crystals were not sufficiently toned to produce fine faceted gems. Many of the geodes with transparent amethyst were broken down to small crystals for the gem trade and this kind of geode is now fairly scarce intact. Many of these geodes were commonly seen for sale in gem shows in the late 1980's and early 1990's, but fewer of them have been seen in the late 1990's. ![]() The most desired hues ranged from deep purplish-red to purple-red and these stones were called Uralian or Siberian Amethyst, terms that are now color grades rather than source areas.Īmethysts from Brazil are mostly extracted from large geodes that are found in basalts of either Triassic or Jurassic age that crop out in the State of Rio Grande do Sul, in the southeastern corner of the country. Historically, the Ural Mountains in Russia produced many fine amethysts and thousands were acquired by Catherine the Great. Most of the amethyst that is used in the gem trade now comes from Brazil. it has refractive indexes ranging from 1.544 to 1.553, it is uniaxial, positive, and may be strongly dichroic in several colored varieties. Quartz in all varieties is Silicon Dioxide, SiO 2, it crystallizes in the hexagonal system, it has a specific gravity of 2.66, and it defines 7 on Mohs hardness scale. Amethyst is the traditional birth stone for the month of February. Color zonation can be very intense in transparent, translucent and opaque varieties. Some translucent to opaque amethyst is also found and the purplish zones alternate with white or grayish areas. Amethyst usually is a transparent variety of quartz that comes in shades of purple.
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