Amethyst (2) Raw Minerals Stones Rocks Collecting

Description

Origin : Brazil

Amethyst 26-40 gr - cm 2-5 Raw Minerals Stones Rocks for Collection.

Amethyst is a purplish variety of quartz, often associated with sub-alkaline basalt rocks, since 3000 BC, in Egypt, South Africa and Mesopotamia, one of the most used gems for the creation of jewelry, seals and carvings. The term derives from the Greek améthystos which means "not drunk". The Greeks believed that it was an excellent remedy for the effects of alcohol and the Romans helped to fuel this belief. A particular behavioral etiquette in fact required diners to drink wine in crystal cups every time the guest brought his to his lips. However, he limited himself to drinking pure water in an amethyst chalice, whose violet reflections 'colored' the water giving it the appearance of wine. Thus the guest could remain elegantly sober while his diners succumbed to intoxication.
However, its purple color has a disadvantage, in fact its prolonged exposure to the sun and intense light causes it to turn pale; at a temperature between 400 ° C and 500 ° C, the crystals change their color in a radical way (in yellow-brown-orange) becoming artificially similar to citrine quartz crystals and often sold fraudulently as such.
Amethyst crystals are found essentially inside geodes developed in basalt rocks due to a subsequent hydrothermal activity, but often close to the magmatic event itself. Geodes are cavities present within igneous rocks, which in fact represent gas bubbles variously shaped by the greater or lesser flow of the magmatic liquid. The lower the viscosity of the liquid, the more elongated can be the shape of the geode of which the sharpest part coincides with the direction of the flow. On the internal walls of these geodes it is possible to develop groups of crystals (among the most common quartz, zeolites, carbonates and sulphates) "grown" thanks to the particular chemical composition and the relatively high temperature (from 850 to 5000 ° C) of the leachate hydrothermal fluids through the rock.
Worldwide, the main deposits of this mineral are found in Brazil, Uruguay, Bolivia, India, Russia, Mexico, USA and Madagascar. In Europe, the most important deposit is that, already discovered in Roman times, of Idar-Oberstein, a town in the Nahe river valley (Germany). In Italy, small formations have been found in the provinces of Trento, Bolzano, Sassari, Grosseto and Turin.
Until a few decades ago with the term Oriental Amethyst, purple corundum of gemological quality was designated; since this terminology could cause confusion with purple amethyst quartz proper, the terminology was changed and therefore that quality of corundum is nowadays defined as "purple sapphire".
Its use is still mainly aimed at the production of jewelry. Until the discovery of the great Brazilian deposits in the 19th century, amethyst was a rare and therefore expensive precious stone, but nowadays it is much cheaper and only the purest and most intense purple large gems can reach high market prices. It is also used to make an inorganic pigment. The crystal differently absorbs the right circular polarized light and it turns; therefore a linearly or circularly polarized light beam will become elliptical after interacting with the crystal. In 1847 the scientist Haidinger thus discovered the effect of circular dichroism, typical of amethysts.