Lorándite

Lorandite is a rarely occurring mineral from the mineral class of " sulfides and sulfosalts ". It crystallizes in the monoclinic crystal system with the composition TlAsS2 ( thallium, arsenic, and sulfur) and is according to the nomenclature of the International Mineralogical Association (IMA ), a binary sulfosalt with a cation / chalcogen ratio of 1: 1 According to the chemical nomenclature according to IUPAC is it is Lorandite a thallium (I) thioarsenit or a thallium (I) thioarsenat (III).

Lorandite usually develops granular to massive aggregates, in rare cases, well-trained, tabular or prismatic to acicular crystals. Fresh samples are of a scarlet color with metallic luster. With time, however, the mineral often runs on lead- gray. However, the stroke color remains visible carmine.

Lorandite is the most abundant mineral thallium.

Etymology and history

Was recognized and described as an independent mineral Lorandite 1894 by József Krenner which has designated it after the Hungarian physicist Loránd Eötvös.

Synthetic crystals can be grown by hydrothermal Transportraktionen

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Lorandite belonged to the mineral class of " sulfides and sulfosalts " and then to the Department of " thio " where he along with Edenharterit, Grumiplucit, Hutchinsonit, Jentschit, Livingstonit, Simonit, Tvalchrelidzeit, Vaughanit, Vrbait and Weissbergit the unnamed group with the system no. II/E.13 formed.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Lorandite also in the class of " sulfides and sulfosalts ," there, however, in the fine already divided the department " sulfosalts with SnS as model " one. This department is also further divided according to the conditions prevailing in the interconnect metals, so that the mineral is found according to its composition in the subsection " Using Thallium (Tl) ", where it is the only member of the unnamed group 2.HD.05.

The mainly common in English-speaking classification of minerals according to Dana assigns the Lorandite in the class of " sulfides and sulfosalts " and there in the department of " thio " one. Here he is the only member in the group 03:07:06 within the subdivision " 03:07 sulfosalts with the ratio z / y = 2 and the composition (A ) i ( A2 ) j [ Bycz ], A ​​= metals, B = semimetals, C = non-metals to find. "

Education and Locations

Lorandite hydrothermally formed at low temperatures and occurs together with Stilbite, realgar, orpiment, cinnabar, Vrabit, Greigerit and marcasite, pyrite, tetrahedrite, sphalerite, native arsenic and barite. The type locality is Allchar in Macedonia. Other known occurrences are Hg -Tl - Au deposits in China ( Xiangquan Tl deposit, Lanmuchang Tl (Hg) deposit, Zimudang Au -Hg ( Tl) deposit ) and the USA (Nevada, Utah, Wyoming), Zarshuran - gold deposit ( Takab, Iran), Beshtau uranium deposit (Caucasus, Russia) as well as the pit Lengenbach (Valais, Switzerland ).

Crystal structure

Lorandite crystallizes in the monoclinic space group P21 / a with lattice parameters a = 12.27 Å, b = 11.33 Å, c = 6.11 Å and β = 104.2 ° and 8 formula units per unit cell.

In the crystal structure of Lorandite each arsenic atom (As) covalently with three sulfur atoms ( S) is connected d ( As-S ) = 2.08 to 2.32 Å), with the sulfur atoms in the base and the arsenic atom at the tip of a trigonal pyramid coordination polyhedron is. Taking into account the stereochemically active lone pair of As (III ) cation, this arrangement can be described as a ψ1 - tetrahedron, with the As atom in the center and the lone pair is a pseudo-ligand in the fourth corner of an imaginary tetrahedron ( see also VSEPR model). This [ ASS3 ] 3 - Thioarsenateinheiten are not isolated in the structure prior to, but are condensed on two common S atoms to the spiral chains of the Niggli formula, along the 21- coil axis in the direction ( parallel to the crystallographic b axis ) run.

The thallium atoms ( Tl) in turn the head of a distorted tetragonal pyramid, whose base is four sulfur atoms (d ( Tl- S) = 2.95 to 3.30 Å) are located. For more bonds to S atoms on the Tl- tips of these pyramids coordination with d '( Tl- S) = 3.36 to 3.87 Å can thereby be taken into consideration, resulting in an Extensions Manager of the Tl coordination spheres to seven with just capped trigonal prisms as coordination polyhedra results. Tl (I ) cations link the individual chains of Thioarsenateinheiten one another, whereby the three-dimensional crystal structure.

Use

The industrial importance of Lorandite is low. In some deposits, it is relevant for the extraction of thallium.

Of scientific interest is Lorandite as a possible dosimeter to measure solar activity since the end of the 20th century. The thallium isotope 205Tl transformed by bombardment with neutrinos in the lead isotope 205Pb to. The determination of 205Pb contents of old Thalluimmineralen thus allows conclusions on the intensity of the neutrino radiation from the sun.