Pyrargyrite is a sulfosalt
Sulfosalt minerals
Sulfosalt minerals are those complex sulfide minerals with the general formula: AmBnSp; where A represents a metal such as copper, lead, silver, iron and rarely mercury, zinc, vanadium; B usually represents semi-metal such as arsenic, antimony, bismuth and rarely germanium, or metals like tin and...

A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 consisting of silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

 sulfantimonide, Ag3SbS3. Known also as dark red silver ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....

 or ruby silver, it is an important source of the metal.

It is closely allied to, and isomorphous with, the corresponding sulfarsenide known as proustite
Proustite is a sulfosalt mineral consisting of silver sulfarsenide, Ag3AsS3, known also as light red silver or ruby silver ore, and an important source of the metal. It is closely allied to the corresponding sulfantimonide, pyrargyrite, from which it was distinguished by the chemical analyses of...

 or light red silver ore. Ruby silver or red silver ore (German Rotgiiltigerz) was mentioned by Georg Agricola
Georg Agricola
Georgius Agricola was a German scholar and scientist. Known as "the father of mineralogy", he was born at Glauchau in Saxony. His real name was Georg Pawer; Agricola is the Latinised version of his name, Pawer meaning "farmer"...

 in 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 the rhombohedral system, possessing the same degree of symmetry as tourmaline
Tourmaline is a crystal boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gem comes in a wide variety of colors...

. 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. Twinning
Crystal twinning
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....

 according to several laws is not uncommon. The hexagonal prisms of pyrargyrite are usually terminated by a low hexagonal pyramid or by a drusy basal 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 the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 pyr and argyros, "fire-silver" in allusion to color and silver content, given by E. F. Glocker in 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. The Mohs hardness is 2.75, and the specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...

 5.85. 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 with calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

, argentiferous galena
Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms...

, native silver, native arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...

, &c. The best crystallized specimens are from Sankt Andreasberg
Sankt Andreasberg
Sankt Andreasberg is a town and a former municipality in the district of Goslar, in Lower Saxony, Germany. Since 1 November 2011, it is part of the town Braunlage. It is situated in the Harz, approximately 7 km west of Braunlage proper, and 20 km east of Osterode am Harz.- History :Sankt...

 in the Harz
The Harz is the highest mountain range in northern Germany and its rugged terrain extends across parts of Lower Saxony, Saxony-Anhalt and Thuringia. The name Harz derives from the Middle High German word Hardt or Hart , latinized as Hercynia. The legendary Brocken is the highest summit in the Harz...

, Freiberg
Freiberg, Saxony
Freiberg is a city in the Free State of Saxony, Germany, administrative center of the Mittelsachsen district.-History:The city was founded in 1186, and has been a center of the mining industry in the Ore Mountains for centuries...

 in Saxony
The Free State of Saxony is a landlocked state of Germany, contingent with Brandenburg, Saxony Anhalt, Thuringia, Bavaria, the Czech Republic and Poland. It is the tenth-largest German state in area, with of Germany's sixteen states....

, and Guanajuato
Guanajuato officially Estado Libre y Soberano de Guanajuato is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 46 municipalities and its capital city is Guanajuato....

 in Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

. It is not uncommon in many silver mines in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, but rarely as distinct crystals; and it has been found in some Cornish
Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...


Although the red silver ores afford a good example of isomorphism, they rarely form mixtures; pyrargyrite rarely contains as much as 3% of arsenic replacing antimony
Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...

, and the same is true of antimony in proustite. Dimorphous with pyrargyrite and proustite respectively are the rare monoclinic species pyrostilpnite or fireblende (Ag3SbS3) and xanthoconite (Ag3AsS3): these four minerals thus form an isodimorphous group.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.