Pyrargyrite
| Pyrargyrite | |
|---|---|
 | |
| General | |
| Category | Sulfosalt |
| Formula (repeating unit) | Ag3SbS3 |
| IMA symbol | Pyg[1] |
| Strunz classification | 2.GA.05 |
| Crystal system | Trigonal |
| Crystal class | Ditrigonal pyramidal (3m) (sameH-M symbol) |
| Space group | R3c |
| Unit cell | a = 11.047Å,c = 8.719 Å; Z = 6 |
| Identification | |
| Color | Deep red to red gray |
| Crystal habit | Include prismatic crystals with rhombohedral and scalenohedral faces forming terminations. massive, granular |
| Twinning | Complex to lammellar |
| Cleavage | Distinct on {1011}, imperfect on {0112} |
| Fracture | Conchoidal, uneven |
| Tenacity | Brittle |
| Mohs scalehardness | 2.5 |
| Luster | Adamantine |
| Streak | dark cherry red |
| Diaphaneity | Translucent to nearly opaque |
| Specific gravity | 5.82 |
| Optical properties | Uniaxial (–) |
| Refractive index | nω= 3.084 nε= 2.881 |
| Birefringence | δ = 0.203 |
| Pleochroism | Distinct |
| Other characteristics | Darkens upon exposure to light; crystals are frequently striated |
| References | [2][3][4] |
Pyrargyriteis asulfosaltmineralconsisting ofsilversulfantimonite, Ag3SbS3.Known also asdark red silver ore,ruby blende,garnete blendeorruby silver,it is an important source of the metal.
It is closely allied to, and isomorphous with, the corresponding sulfarsenide known asproustiteor light red silverore.Ruby silver or red silver ore (GermanRotgültigerz) was mentioned byGeorg Agricolain 1546, but the two species so closely resemble one another that they were not completely distinguished until chemical analyses of both were made.
Both crystallize in the ditrigonal pyramidal (hemimorphic-hemihedral) class of therhombohedral system,possessing the same degree of symmetry astourmaline.Crystals are perfectly developed and are usually prismatic in habit; they are frequently attached at one end, the hemimorphic character being then evident by the fact that the oblique striations on the prism faces are directed towards one end only of the crystal.Twinningaccording to several laws is not uncommon. The hexagonal prisms of pyrargyrite are usually terminated by a low hexagonal pyramid or by a drusybasal plane.
The color of pyrargyrite is usually greyish-black and the lustre metallic-adamantine; large crystals are opaque, but small ones and thin splinters are deep ruby-red by transmitted light, hence the name, from theGreekpyrandargyros,"fire-silver" in allusion to color and silver content, given byE. F. Glockerin 1831. The streak is purplish-red, thus differing markedly from the scarlet streak of proustite and affording a ready means of distinguishing the two minerals. TheMohs hardnessis 2.75, and thespecific gravity5.85. The refractive indices (nω = 3.084 nε = 2.881) and birefringence (δ = 0.203) are very high. There is no very distinct cleavage and the fracture is conchoidal. The mineral occurs in metalliferous veins withcalcite,argentiferousgalena,native silver, nativearsenic,etc. The best crystallized specimens are fromSankt Andreasbergin theHarz,FreiberginSaxony,andGuanajuatoinMexico.It is not uncommon in many silver mines in theUnited States,but rarely as distinct crystals; and it has been found in someCornishmines.
Although the red silver ores afford a good example of isomorphism, they rarely form mixtures; pyrargyrite rarely contains as much as 3% of arsenic replacingantimony,and the same is true of antimony in proustite. Dimorphous with pyrargyrite and proustite respectively are the raremonoclinicspeciespyrostilpniteorfireblende(Ag3SbS3) andxanthoconite(Ag3AsS3): these four minerals thus form an isodimorphous group.
References
[edit]- ^Warr, L.N. (2021)."IMA–CNMNC approved mineral symbols".Mineralogical Magazine.85(3): 291–320.Bibcode:2021MinM...85..291W.doi:10.1180/mgm.2021.43.S2CID235729616.
- ^Pyrargyrite in the Handbook of Mineralogy
- ^Pyrargyrite on Mindat.org
- ^Pyrargyrite data on Webmineral
This article incorporates text from a publication now in thepublic domain:Chisholm, Hugh,ed. (1911). "Pyrargyrite".Encyclopædia Britannica.Vol. 22 (11th ed.). Cambridge University Press. pp. 685–686.
