Alacranite
| Alacranite | |
|---|---|
 |
|
| General and classification | |
| other names |
IMA 1985-033 |
| chemical formula | As 8 S 9 |
|
Mineral class (and possibly department) |
Sulfides and sulfosalts |
|
System no. to Strunz and to Dana |
2.FA.20 ( 8th edition : II / F.02) 08/02/22/04 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Room group (no.) | P 2 / c (No. 15) |
| Lattice parameters |
a = 9.942 Å ; b = 9.601 Å; c = 9.178 Å β = 101.94 ° |
| Formula units | Z = 2 |
| Physical Properties | |
| Mohs hardness | 1.5 |
| Density (g / cm 3 ) | measured: 3.43 (3); calculated: 3.503 |
| Cleavage | imperfect after {100} |
| Break ; Tenacity | clamshell; very brittle |
| colour | orange to light gray with inner, yellow-pink reflections |
| Line color | orange yellow |
| transparency | transparent to translucent |
| shine | Diamond luster, glass luster, resin luster, fat luster |
| Crystal optics | |
| Refractive indices |
n α = 2.390 (1) n γ = 2.520 (2) |
| Birefringence | δ = 0.130 |
| Optical character | biaxial positive |
Alacránite is a very rarely occurring mineral from the mineral class of " sulfides and sulfosalts ". It crystallizes in the monoclinic crystal system with the chemical composition As 8 S 9 , so it is chemically an arsenic sulfide .
Alacránite is transparent to translucent and is usually found in the form of granular mineral aggregates of orange to light gray color with inner, yellow-pink reflections. Well-developed crystals are less common, only about a millimeter in size and have a tabular to prismatic habit . The crystal faces can be striped parallel to the c-axis.
Etymology and history
Alacránite was first discovered, but only imprecisely determined in 1970 by A. Clark in a silver mine near Alacrán near Tierra Amarilla in the Chilean province of Copiapó . According to Clark, the material found was a realgar-like compound with X-ray properties similar to the high-temperature polymorph of As 4 S 4 as described by Hall in 1966.
VI Popova, VA Popov, A. Clark, VO Polyakov and SE Borisovskii found the mineral in 1986 in paragenesis with realgar and uzonite in the Uzon caldera on the Russian peninsula of Kamchatka and determined the exact composition As 8 S on the basis of electron microprobe analysis 9 . Popova et al. provided a detailed mineralogical description which, along with the name chosen from the earlier site, was recognized by the International Mineralogical Association (IMA).
classification
In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the alacranite belonged to the mineral class of "sulphides and sulphosalts" and there to the general division of "non-metallic sulphides", where together with auripigment , dimorphine , duranusite , laphamite , pararealgar , Realgar and Uzonit formed the unnamed group II / F.02 .
The 9th edition of Strunz's mineral systematics, which has been in force since 2001 and is used by the International Mineralogical Association (IMA), also assigns Alacránite to the class of “sulfides and sulfosalts”, but in the “sulfides of arsenic, alkalis” class; Sulphides with halides, oxides, hydroxides, H 2 O “. This section is further subdivided according to the elements that characterize the compound, so that the mineral can be found according to its composition in the sub-section "with As, (Sb), S", where it is the only member of the unnamed group 2.FA.20 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the alacranite to the class of "sulfides and sulfosalts" and there to the department of "sulfide minerals". Here he is together with Pararealgar, Realgar and Uzonit in the "Realgar group" with the system no. 02.08.22 within the subsection " Sulphides - including selenides and tellurides - with the composition A m B n X p , with (m + n): p = 1: 1 ".
Education and Locations
Alacránite forms either in hydrothermal As-S veins , in the condensation zone of hydrothermal Hg-Sb-As systems as cement in sandy gravel or at low temperatures in polymetallic hydrothermal deposits . Accompanying minerals in addition to realgar and uzonite include acanthite , arsenic , arsenolamprite , arsenopyrite , auripigment , barite , calcite , chalcopyrite , cinnabarite , galena , greigite , pyrite , quartz , solid sulfur , sphalerite and stibnite .
As a rare mineral formation, Alacránite has so far (as of 2012) only been proven at a few sites, with around 20 sites being known. The two places Alacrán and Uzon, which are considered type localities, are so far the only known sites in Chile and Russia.
In Germany, the mineral has so far been found in a quarry in Tiefengraben near Reinerzau and in the mines “Sophia”, “Johann” and “St. Anton “near Wittichen in Baden-Württemberg; in the “Morgenröthe” mine near Eisern in North Rhine-Westphalia; at Hänichen and Possendorf in Saxony and at Culmitzsch in Thuringia.
Other sites are among others in Bulgaria ( Rhodope Mountains ), Japan ( Honshū ), Papua New Guinea ( Lihir Islands ), Romania (Lăzăreşti, Harghita) and the Czech Republic ( Vrchlice , Radvanice v Čechách ).
Crystal structure
Alacránite crystallizes monoclinically in the space group P 2 / c (space group no. 15) with the lattice parameters a = 9.942 Å ; b = 9.601 Å; c = 9.178 Å and β = 101.94 ° as well as 2 formula units per unit cell .
See also
literature
- VI Popova, VA Popov, A. Clark, VO Polyakov and SE Borisovskii: Alacránite, As 8 S 9 - a new mineral , in: Zapiski Vsesoyuznogo Mineralogicheskogo Obshchestva , Volume 115, Chapter 3, pp. 360–368 (Russian, PDF 541 , 9 kB )
Web links
Individual evidence
- ↑ a b IMA / CNMNC List of Mineral Names - Alacránite (PDF 1.8 MB; p. 5)
- ↑ a b c American-Mineralogist-Crystal-Structure-Database - Alacránite (2003)
- ↑ a b Webmineral - Alacránite
- ↑ a b c John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols: Alacránite , in: Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 60.9 kB )
- ↑ a b c Mindat - Alacránite
- ↑ a b PC Burns, JB Percival (2001): Alacranite, As 4 S 4 : a new occurrence, new formula, and determination of the crystal structure , in: The Canadian Mineralogist , Volume 39, pp. 809-818 ( PDF 780 , 6 kB )
- ↑ Mindat - Number of localities for Alacránite