Realgar ( fr. Réalgar , from Arabic: rajj al ghar, literally - the dust of a cave, mine) is a mineral with the chemical composition of arsenic monosulfide AsS.
| Realgar | |
|---|---|
 | |
| Formula | Ass |
| Physical properties | |
| Colour | Bright red, orange, crimson |
| Trait color | Orange |
| Shine | Bold, Diamond |
| Transparency | Transparent, translucent |
| Hardness | 1,5-2 |
| Cleavage | Average for {010} |
| Kink | Crayfish |
| Density | 3.56-3.59 g / cm³ |
| Syngonia | Monoclinic |
| Refractive index | 2.42 |
The crystal structure is complex; built from individual As 4 S 4 molecules; sulfur ions form a square, and arsenic - a tetrahedron; the centers of the square and tetrahedron coincide. It crystallizes in monoclinic syngony, forming prismatic crystals. The color of the realgar is from fiery red to orange-yellow. It is usually found in the form of continuous granular masses, thin veins, inclusions or powdery earthy clusters.
Red arsenic sulfide As 2 S 2 - ancient paint . Pliny mentions her under the name "sandarak." Chennini describes her, but does not particularly praise her. This pigment in the old painting is quite rare, and since the second half of the XIX century is practically not found.
Transparent, fragile, poisonous .
Origin
The origin of low - temperature hydrothermal . Realgar is usually found with auripigment or with antimonite ; as a minor impurity, sometimes also with lead , silver and gold ores. It is also found as a product of sublimation during volcanic eruptions and in the form of deposits from hot springs. Under the influence of sunlight, it decomposes and turns into a yellow powder from a mixture of the auripigment As 2 S 3 and arsenolite As 2 O 3 .
Deposits
Realgar deposits are found in Transcaucasia (Elbrus mine); abroad - in Georgia, Kyrgyzstan, Czechoslovakia , Romania , Greece , USA , Japan and other countries.
In relatively large quantities, realgar is found as a satellite of an auripigment in auripigment veins and is mined with it as ore to produce metallic arsenic (contains 70.1% As).
Application
It is used as an additive to increase the heat resistance of copper , in the production of lead shot , some printing alloys , as well as arsenic- cadmium babbits . Used in tempera painting as an orange mineral pigment .
Sometimes realgar is found during archaeological excavations - in the burials of nomads in southern Russia.
Toxicity
The mineral contains arsenic, therefore it is toxic, like all other arsenic compounds.
Links
- Realgar in webmineral.com database
- Realgar in the catalogmineralov.ru database (rus.)
- Realgar // Big Soviet Encyclopedia : [in 30 vol.] / Ch. ed. A.M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.
- “Arsenic sulfide forms three different liquids”, “Elements”, 04.16.2008
- VV Brazhkin, Y. Katayama, MV Kondrin, T. Hattori, AG Lyapin, H. Saitoh, AsS Melt Under Pressure: One Substance, Three Liquids // Phys. Rev. Lett. 100, 145701 (April 8, 2008).