Realgar
| Realgar | |
|---|---|
 |
|
| General and classification | |
| chemical formula | As 4 S 4 |
|
Mineral class (and possibly department) |
non-metallic sulphides |
|
System no. to Strunz and to Dana |
2.FA.15a ( 8th edition : II / F.02) 08/02/22/01 |
| Similar minerals | Auripigment , Pararealgar , Cinnabarite , Ruby |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic 2 / m |
| Physical Properties | |
| Mohs hardness | 1.5 to 2 |
| Density (g / cm 3 ) | 3.6 |
| Cleavage | imperfect |
| Break ; Tenacity | shell-like |
| colour | red, orange-red |
| Line color | red to orange-yellow |
| transparency | transparent to translucent |
| shine | Diamond luster, fat luster |
| Crystal optics | |
| Refractive indices |
n α = 2.538 n β = 2.684 n γ = 2.704 |
| Birefringence | δ = 0.166 |
| Optical character | biaxial negative |
| Pleochroism | dark red-dark red-orange-red |
| Other properties | |
| Chemical behavior | Partly soluble in acids and potassium hydroxide |
| Special features | highly toxic |
Realgar , Rubin sulfur , red arsenic , as a pigment as Rauschrot , is a common arsenic - sulfur - mineral from the mineral class of the non-metal-like sulfides . It crystallizes in the monoclinic crystal system with the chemical formula As 4 S 4 and develops prismatic, longitudinally striped crystals or granular, massive aggregates in the colors red to orange-yellow.
Etymology and history
The name Realgar comes from the Arabic rahdsch al-ghar /رهج الغار / rahǧ al-ġār and means something like "cave powder" because this mineral was extracted from mines. An alternative name origin is discussed as a reading error from the Arabic rhag al-far (powder rats), which indicates its use as a rat poison .
The first description was carried out by Johan Gottschalk Wallerius , a Swedish chemist and mineralogist in 1747. The type locality is not defined as Realgar was already known in antiquity.
Special properties
Realgar is very unstable and decomposes in the air under the action of light in the visual spectral range into auripigment (As 2 S 3 ) and arsenic (As 2 O 3 ) or pararealgar (AsS). It is partially soluble in acids and in potassium hydroxide solution and develops toxic fumes that smell like garlic . The resulting gas is arsine .
Realgar can be easily melted in front of the soldering tube , burning with a bluish-white flame and also developing a strong smell of garlic.
Realgar has a certain similarity in color to cinnabar (vermilion) and ruby . However, both crystallize trigonally and are either much heavier or harder than realgar.
classification
In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the realgar belonged to the mineral class of "sulfides and sulfosalts" and there to the general division of "non-metallic sulfides", where together with alacranite , dimorphine , duranusite , laphamite , auripigment , Pararealgar and Uzonit formed a common group.
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns the realgar to the class of “sulfides and sulfosalts”, but in the section of “sulfides of arsenic, alkalis; Sulphides with halides, oxides, hydroxides, H 2 O “. This section is also more precisely subdivided according to the type of elements contained in the formula, so that the mineral can be found according to its composition in the sub-section "with As, (Sb), S", where it, only together with Pararealgar, is the unnamed Forms group 2.FA.15 .
The systematics of minerals according to Dana also assigns the realgar to the class of "sulphides and sulphosalts" and there into the category of "sulphide minerals". Here it is the eponymous mineral of the "Realgar group" with the system no. 02.08.22 and the other members Alacránit, Pararealgar and Uzonit within the subdivision of " Sulphides - including selenides and tellurides - with the general composition A m B n X p , with (m + n): p = 1: 1 ".
Education and Locations
As a typical secondary mineral , realgar is found together with the related aura pigment in hydrothermal veins and springs. It is created by the decomposition of other arsenic-containing minerals such as arsenopyrite , but also by resublimation of volcanic gases.
So far (as of 2010) Realgar has been found at around 500 sites worldwide. Important sites are the Lengenbach mine in the Binn valley , the canton of Valais in Switzerland , Baia Sprie and Transylvania in Romania , Shimen / Hunan in China , Nevada in the USA and Allchar in Macedonia .
Crystal structure
The unit cell of the chemical compound is cage-shaped, with strong, covalent bonds in the crystal within the cages and weak van der Waals bonds between the cages , which explains the chemical instability. In the individual cage, the arsenic atoms ( oxidation level : +2) are each connected to a further arsenic and two sulfur atoms. The sulfur atoms (oxidation state: −2) each have 2 bonds to arsenic atoms.
use
Realgar was used as a pigment in ancient times because of its immiscible orange-red color . It can also be found in medieval book and panel painting ; Titian used it e.g. B. in the cymbal player's coat in the oil painting Bacchus and Ariadne (made 1520–23). In the Middle Ages, realgar was also used in medicine and in glass production . For example, realgar was used in Taoist statues in the past. The Taoists' handling of the statues cured them of parasite infestations, as the amount of arsenic absorbed was sufficient to kill the parasites , but not lethal for the Taoists. For this reason, the statues in Taoism were ascribed a healing effect.
Today, due to its extreme toxicity, it may only be used as a pigment in exceptional cases and under special safety precautions. It is still available from specialist retailers for special restoration applications . For other purposes it can be replaced by modern synthetic pigments such as tar dyes ( perylene red ). It is also used today in pyrotechnics , but also in pesticide production.
Precautions
Realgar contains a high proportion of arsenic of approx. 70 percent by weight and is therefore classified as a toxic substance ( H-phrases H301 toxic if inhaled , H331 toxic if swallowed , H410 very toxic to aquatic organisms with long-term effects ). Precise information about the toxicity is hardly possible, since a decomposition product of realgar in the air is arsenic , which, due to its good solubility, has a significantly higher toxicity than pure arsenic. The orally ingested, lethal dose for humans can be less than 0.1 g.
Handling realgar requires special precautions, such as keep locked up; Use protective gloves, face mask and eye protection; Do not eat, drink or smoke at work; Avoid release to the environment and dispose of as hazardous waste. When transporting relevant quantities, it falls under dangerous goods class 6.1 with hazard number 60 above UN number 1557.
See also
swell
- ↑ Karl Lokotsch: Etymological dictionary of European [...] words of oriental origin. Carl Winter, Heidelberg 1927, p. 135
- ^ Center National of the resource Textuelles et Lexicales: Realgar french
- ↑ DL Douglass, Chichang Shing: The light-induced alteration of realgar to pararealgar , In: American Mineralogist , Volume 77 (1992), pp. 1266–1274 ( PDF 1.1 MB )
- ^ Paul Ramdohr , Hugo Strunz : Klockmanns textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 482 .
- ↑ Mindat - Localities for realgar
- ↑ M.Binnewies: Allgemeine und inorganic Chemie, Spektrum Verlag, 2004
- ↑ Master Pigments - Realgar ( Memento from March 15, 2014 in the Internet Archive )
- ↑ Rayner-Canham, Geoffrey; Overton, Tina: Descriptive inorganic chemistry. New York 2010. page 16
- ↑ Entry for CAS no. 1303-33-9 in the GESTIS substance database of the IFA , accessed on November 3, 2015 (JavaScript required)
literature
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 .
- Martin Okrusch, Siegfried Matthes: Mineralogy: An introduction to special mineralogy, petrology and deposit science . 7th edition. Springer Verlag, Berlin, Heidelberg, New York 2005, ISBN 3-540-23812-3 .
- Karl Krüger: The realm of minerals and rocks . Safari Verlag., Berlin, ISBN 3-7934-1339-X .
