10/29/2022 0 Comments Lace amethyst gemstone![]() ![]() Chrome-bearing fuchsite (a variety of muscovite mica) is the classic inclusion, and gives a silvery green or blue sheen. The most common colour of aventurine is green, but it may also be orange, brown, yellow, blue, or gray. In no case would this iridescence have been visible during the animal’s life additional shell layers covered it.Īventurine is a form of quartz, characterised by its translucency and the presence of platy mineral inclusions that give a shimmering or glistening effect termed aventurescence. These iridescent ammonites are often of gem quality (ammolite) when polished. Other fossils, such as many found in Madagascar and Alberta (Canada), display iridescence. ![]() Often the name of an ammonite genus ends in -ceras, which is Greek (κρας) for “horn” (for instance, Pleuroceras). near Pompeii) called fossils of these animals ammonis cornua (“horns of Ammon”) because the Egyptian god Ammon (Amun) was typically depicted wearing ram’s horns. Their name came from their spiral shape as their fossilized shells somewhat resemble tightly-coiled rams’ horns. Their fossil shells usually take the form of planispirals, although there were some helically-spiraled and non-spiraled forms (known as “heteromorphs”). They are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific geological time periods.Īmmonites’ closest living relative is probably not the modern Nautilus (which they outwardly resemble), but rather the subclass Coleoidea (octopus, squid, and cuttlefish). Amazonite is usually light green to blue-green, mottled and sometimes contains light striations.Īmmonites are an extinct group of marine animals of the subclass Ammonoidea in the class Cephalopoda, phylum Mollusca. This causes an interference effect of light.Īmazonite is found in the United States, Brazil, Zimbabwe, Russia, Australia, Namibia. Orthoclase feldspar and albite are present in close association, arranged in layers. ![]() The schiller is caused by a feature of the stone's crystal structure. Schiller is a lustrous reflection from planes in a mineral grain and is similar to what is more commonly known as iridescence. It displays a schiller of light which is caused by inclusions. (Hoffmeister and Rossman, 1985.Īmazonite is a gem variety of microcline feldspar and is usually polished as a cabochon. More recent studies suggest that the blue-green color results from small quantities of lead and water in the feldspar. Naturally, many people assumed the color was due to copper because copper compounds often have blue and green colors. ![]() Some other localities in the United States yield amazonite, and it is also found in pegmatite in Madagascar.īecause of its bright green colour when polished, amazonite is sometimes cut and used as a gemstone, although it is easily fractured.įor many years, the source of amazonite's color was a mystery. Crystal Peak, Teller County, Colorado is a well-known locality for crystals of amazonite. More recently, high-quality crystals have been obtained from Pike's Peak, Colorado, where it is found associated with smoky quartz, orthoclase, and albite in a coarse granite or pegmatite. Formerly it was obtained almost exclusively from the area of Miass in the Ilmen mountains, 50 miles southwest of Chelyabinsk, Russia, where it occurs in granitic rocks. The name is taken from that of the Amazon River, from which certain green stones were formerly obtained, but it is doubtful whether green feldspar occurs in the Amazon area.Īmazonite is a mineral of limited occurrence. Amazonite (sometimes called “Amazon stone”) is a green variety of microcline feldspar. ![]()
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