Sylvanite

Sylvanite, outdated also known as Schrifterz, Aurotellurid, Goldschmidtit or Weißgolderz, is a rarely occurring mineral from the mineral class of sulfides and sulfosalts. It crystallizes in the monoclinic crystal system with the chemical composition ( AuAg ) 2Te4 and developed up to a centimeter large crystals, which are usually grown dendritic or laminate. The mineral is of gray to white in color.

Special Features

Sylvanite is one of the few minerals in which gold occurs naturally in the form of a connection. This is because that the precious metal gold only with the rare metalloid tellurium forms stable compounds, while other gold compounds readily decompose to form elemental gold.

Sylvanite easily melts before the blowpipe. This white smoke occurs and initially are formed gray - metallic beads. After a long time, finally forms a brilliant and deformable bead.

The mineral separates in nitric acid and aqua regia gold silver chloride ( silver chloride ).

Etymology and history

Sylvanite was the first time in 1798 in Baia de Aries a major before the closure in 2004 of gold -tellurium deposit in Romania found. Martin Heinrich Klaproth it was first established, and set a fixed ratio of gold to silver to tellurium of 30:10:60. Abraham Gottlob Werner called it Schrifterz, since the arrangement of crystals partially reminiscent of drawings. The name was given to the mineral sylvanite of Louis Albert Necker, who, it is to Transylvania, the ancient name of the region in the Baia de Aries, named.

Classification

In the classification by Strunz sylvanite is classified in the sulfides and sulfosalts. It is counted among the sulfides with a ratio of metal to sulfur, selenium or tellurium of < 1:1 or 1:2. In the eighth edition, it made with Calaverit, Kostovit and Krennerit a group. In the ninth edition of the sulfides can be further divided by cations, where it forms sylvanite own sub- group of metal sulfides with a ratio of metal to sulfur, selenium or tellurium, of 1:2, and copper, silver, gold, nickel, tin, platinum group metals, molybdenum, or tungsten.

In the classification of minerals according to Dana it forms with Krennerit, Calaverit and Kostovit a subset of the sulfides - tellurides and selenides, including - with the composition AmBn Xp, with (m n): p = 1:2.

Education and Locations

The mineral usually forms at low temperature under hydrothermal conditions. It is one of the last minerals formed. Sylvanite is associated with gold, Calaverit, Krennerit, Altait, hessite, petzite, acanthite, pyrite, galena, sphalerite, chalcopyrite, quartz and fluorite.

Sylvanite is found in small quantities in many gold-silver deposits, but larger, economically exploitable deposits are rare. Among the localities include Baia de Aries, Sǎcǎrîmbu and Facebanya in Romania, Glava in Sweden, the southern Urals in Russia, Porcupine in Canada, various mines in the United States about Cripple Creek or Gold Hill, Sonora, Mexico, Kalgoorlie in Australia, Negros Occidental in the Philippines, Guyana and Fiji.

Crystal structure

Sylvanite crystallizes in the monoclinic crystal system, space group P2 / c with lattice parameters a = 8.95 Å; b = 4.478 Å, c = 14.62 Å and β = 145.35 ° and two formula units per unit cell.

Use

Larger deposits of sylvanite be mined as a raw material for the extraction of gold and tellurium.