Amethyst

AMETHYST (from the Greek word "amethystos", which means "sober", "not intoxicated"; it was used as the amulet against intoxication * EN: amethyst; DE: Amethyst; FR: amethyste; ES: amatista; RU: аметист) is mineral, violet variety of quartz. The shades of the colouration are from the blue-violet, lavender-blue, to the most valued purple-dark-violet. There also occur the violet-smoky amethysts. The distribution of the colouration is usually uneven: zonal (the intensely coloured zones are parallel to the faces of the rhombohedrons) or spotty. During the heating, certain amethysts become golden-yellow or greenish-yellow (the method of the artificial obtainment of the "Madeiran" topazes for the jewellery, and of the other varieties). The colouration of the amethysts is associated with the ions of iron, which are replacing silicon, and are in the tetravalent state, which is unusual for iron.

The habitus of amethyst is: short-prismatic crystals with dominant rhombohedral faces, or sceptre-shaped crystals, which are formed by the overgrowth of the short-prismatic amethyst onto the long-prismatic quartz (Ural type), and also the obelisk-shaped prismatic crystals (Uruguayan and Brazilian types). There are common the multiple-domed crystals and intergrowths of the block structure. The sizes are from microscopic to 10-30 centimetres. Amethyst is the low-temperature hydrothermal mineral. The main deposits are represented by the zones of the mineralized cracks within granites and syenites (Zambia, Zimbabwe, and within the USSR, Vatikha at the Middle Urals), rock-crystal-bearing quartz veins within quartzites and schists (Brazil; within the USSR, Khosavarkha, at the Urals) and post-volcanic agate-amethyst geodes within basalts (Brazil, Uruguay, Argentina).

Amethyst also occurs within the miarolitic granitic pegmatites, iron ore skarns and other formations. Residual eluvial and diluvial-alluvial placer deposits of amethysts are known within Africa, Asia, and South America; within the USSR, at the Urals and within Uzbekistan. There is named as the "amethyst-like quartz" the drainage veinous quartz with uneven amethyst-like colouration; amethyst belongs to the precious gemstones of the IV order; the amethyst-like quartz and drusen (so called brushes) of the small (0.3-1.0 centimetres) crystals belong to the jewellery-ornamental stones. There has been performed within the USSR for the first time within the world the industrial synthesis of amethyst from the aqueous solutions of silica, there is conducted the ennoblement (the continued overgrowing by amethyst) of the drusen of the natural crystals of quartz.