Amethyst Source & Occurrence loose sale price & Amethyst Gemstone Information
Amethyst is mined in Brazil, Uruguay, Bolivia and Argentina, as well as in Zambia, Namibia and other African countries.
Amethyst has been found in siliceous volcanics, occurring as macroscopic crystals and drusy coverings inside of agate lined amygdaloidal cavities or vugs, often forming geodes. Amethyst also occursin quartz veins. The purple color of amethyst is due to small amounts (approximately 40 parts per million) of iron (Fe4+) impurities at specific sites in the crystal structure of quartz. The difference between amethyst and citrine is only the oxidation state of the iron impurities present in the quartz. Upon heating, the iron impurities are reduced and amethyst's purple color fades and becomes yellow to reddish-orange (citrine), green, or colorless depending on the site and original oxidation state of the iron impurities present and the amount and duration of the heating. The amethystine color usually can be regained by irradiation which re-oxidizes the iron impurities. This irradiation can be done by synthetic means, or it can occur in nature by radioactive decay of nearby radioactive minerals. In most cases this is a reversible process, however excessive heating may change the distribution of the iron impurities at the different sites within the quartz making it impossible to convert it back to amethyst by subsequent irradiation. The heating process can occur naturally or synthetically. At the present, it is not possible to determine whether or not an amethyst or citrine was synthetically irradiated or heated. Amethyst is recognized by its color, crystal habit, occurance, hardness, glassy luster, conchoidal fracture and lack of cleavage.
Vera Cruz, Mexico -- very pale, clear, prismatic crystals that are sometimes double terminated and have grown on a light colored host rock. Crystals are typically phantomed, having a clear quartz interior and an amethyst exterior. Some are sceptered and phantomed.
Guerrero, Mexico -- dark, deep purple, prismatic crystals that radiate outward from a common attachment point. Often the crystals are phantomed opposite of Vera Cruz amethyst having a purple interior with a clear or white quartz exterior. These are some of the most valuable amethysts in the world.
Minas Gerais and Rio Grande do Sul, Bahaia, Brazil -- crystals form in druzy crusts that line the inside of sometimes large volcanic rock pockets or "vugs". Some of the vugs form from trees that were engulfed in a lava flow millions of years ago and have since withered away. Other vugs are just gas bubbles in the lava. Some vugs can be quite large. The crystals that form are usually light to medium in color and only colored at the tops of the crystals. Most clusters form with gray, white and blue agate and have a green exterior on the vugs. Calcite sometimes is associated and inclusions of cacoxenite are common.
Maraba, Brazil -- large crystals with unattractive surfaces that are of a pale to medium color and often carved or cut into slices.
Thunder Bay, Canada -- a distinct red hematite inclusion just below the surface of the crystals is unique to this locality. Clusters are druzy crusts that line the fissures formed in ancient metamorphic rocks.
Uruguay -- crystals are dark to medium and form in druzy crusts that line the inside of volcanic vugs that have a gray or brown exterior. The crystals are usually colored throughout, unlike the Brazilian crystals, and form with a multicolored agate that often contains reds, yellows and oranges. Often amethyst- coated stalactites and other unusual formations occur inside these vugs.
Africa -- crystals are usually large but not attractive. However, the interior color and clarity are excellent and polished slices and carvings as well as many gemstones are prized and admired.
Maine, USA -- Dark druzy clusters that are not widely distributed today.
North Carolina, USA -- Druzy clusters that have a bluish-violet tint.
Pennsylvania, USA -- druzy clusters that filled fractures in metamorphic rocks. They are generally a brownish purple and patchy in color.
Colorado, USA -- druzy clusters form crusts inside of fissures in sandstone, often on top of a crust of green fluorite. Crystals are dark but rather small.
Italy -- both Vera Cruz like crystals, although not as well defined, and large parallel growth clusters with good evenly distributed color.
Germany -- associated with colorful agates that form a druzy light-colored crust.
Ural Mountains, Russia -- a very clear and dark variety that is cut for fine expensive gemstones, natural uncut clusters.
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