Mineral Argentite
The chemical composition of mineral Argentite is indicated by the formula Ag2S, Silver Sulfide. This mineral Argentite belongs to the Sulfides mineral class. Sulfide minerals are commonly considered economically important as metal ores. It is considered as the most major ore of important metals like silver, lead, gold, and copper. Sulfide ore mineral samples are commonly evaluated under an ore light polarizing microscope. Argentite is said to be a high temperature form of mineral Acanthite. The crystal structure of Argentite crystals is actually found unstable at temperatures below 356ºF or 180ºC. At temperatures below 180ºC, the crystal structure of Argentite mineral changes to that of Acanthite. It is said that Argentite mineral is commonly pseudomorphous after mineral Acanthite. This means that Argentite mineral crystals are actually Acanthite crystals, which only appear in the shape of Argentite crystals. Acanthite minerals are considered most important silver ore next to galena. Silver content in the ore mineral sample is actually visible when ore samples are examined with the aid of ore light polarizing microscopes. Argentite minerals are also considered belonging to the galena group. Galena is a lead ore that is commonly considered containing enough silver, which is usually about 1%. It has been known that after the lead processing, the by-product silver is commonly used as a major supply to the world’s needs. Argentite is considered as an important constituent of silver ore deposits. It is commonly found having 87 percent silver content. Its common form is usually in blackish-gray coatings or masses, which are majestically exhibited under polarized microscopes.
G. Agricola already mentioned this mineral specie so long ago in the year 1529. Argentite mineral derived its name from a Latin word “argentums”, which means silver. The symbol Ag for silver was also derived from this word. This name Argentite however was not used until year 1845. W. Von Haidinger named the new mineral species as Argentite. This is relative to the lead gray color of the mineral species, which can be splendidly exhibited and optically evaluated with the aid of petrographic polarizing microscope. This species do have other old names such as silverglance, vitreous silver, and Glaserz. Jalpaite is considered as a cupriferous variety of Argentite, which is usually found in Tobasco, Mexico. Argentite and Acanthite minerals said to be polymorphs. They have the same chemistry but with different structure. The name Argentite actually refers to the high temperature form of silver sulfide, which is only stable at temperatures above 180ºC. Some guidebooks states that the name Argentite is commonly used by some who are confused to describe the pseudo-cubic crystals of silver sulfide or Acanthite where the original crystal form of the high temperature Argentite mineral has remained. It has been also noted that Acanthite crystal is a supposed dimorphous form, which is commonly found crystallizing in the orthorhombic system as exhibited under light polarizing microscope for geologists. It is said also that the crystals of Acanthite mineral are probably distorted crystals of mineral Argentite.
Argentite minerals are occasionally found displaying structural units in forms of uneven cubes, and they are commonly exhibiting cubic and octahedral crystal habits, which are clearly visible under geological light polarizing microscopes. They may also be found showing dodecahedral form and sometimes may appear modified or distorted when viewed with the aid of geological polarized light microscopes. Some crystals may be found branching and reticuled, commonly in massive forms. They may form interesting crystal groupings, which are often distorted but forming together as a group into some intricate arborescent or branching structures, which are splendidly exhibited under an ore light polarizing microscope. They often found in earthy masses or as dendritic. They can be found in granular forms and sometimes as coatings in reflected light of polarized microscopes. They may also exhibit blocky habit where crystal shape tends to be equant. Sometimes they may also appear in skeletal crystal form where crystals form crude outlines with missing faces in reflected light of petrographic light polarizing microscope. When this Argentite mineral is found in large masses, they are commonly considered forming an important ore of silver. Argentite mineral, like other sulfides, tellurides, and selenides of copper and silver, is known to crystallize in isometric crystal formation at high temperatures. When these Argentite crystals cool down, they actually invert readily from being isometric in form to being monoclinic in structure leaving its external appearance unchanged. The isometric system is known to comprise crystals having three axes, which are usually found perpendicular to one another and all in equal lengths. The monoclinic system on the other hand, comprises crystals having three axes, which are unequal in lengths, two of which are found not perpendicular but rather oblique to one another, but both of which are commonly found perpendicular to the third axis. It is considered dimorphous with mineral Acanthite. Argentite crystals are commonly opaque in appearance. These Argentite minerals are usually associated with native silver, cerussite, and chlorargyrite. Argentite is generally considered as a very valuable mineral specimen. Maybe this is due to the high silver content and its rare well-formed crystals.
Argentite minerals commonly occur exhibiting a blackish lead gray color by the naked eye or even with the aid of petrographic polarizing microscope in reflected light. They may also appear in dark gray or in nearly black color in hand samples. This mineral Argentite is commonly found sectile, which means it can be cut into by a knife just like lead. It usually exhibits shining streak, which is commonly in shiny black, when rubbed on a white streak plate. Argentite minerals usually lack distinct cleavage. The cubic cleavage, which is usually considered as a prominent feature of a Galena mineral is commonly found present in Argentite but only in traces. This cleavage lines are usually visible when mineral is viewed under geological light polarizing microscope. Argentite mineral usually have poor cleavages in two different directions. The relative hardness measure of mineral Argentite using the Mohs scale method is usually 2.5, which is considered soft. Argentite specimens are usually cuttable, bendable, and malleable. This mineral Argentite has strong metallic appearance. Argentite is commonly known to exhibit metallic luster in reflected light of petrographic polarizing microscope because it has high reflectivity like metals. The fresh and shiny surface of Argentite will eventually form a dull coating after prolonged exposure to light. It may appear dull if mineral tarnished severely. Argentite mineral specimens are commonly found having specific gravity of 7.3g/cm³, which is considered slightly heavy even for metallic minerals. The fracture found is commonly conchoidal between crossed nicols of polarized light microscopes. This commonly shows a smooth curved fracture with concentric ridges of the type shown by glass. Mineral specimens of Argentite are commonly known as nonmagnetic. It has been found that when mineral specimen of Argentite is heated on charcoal, it commonly yields a small mass of silver metal.
Argentite minerals are commonly occur disseminated in galena and in the cementation zone of lead and zinc deposits. It can be found occurring in some hydrothermal ore veins of low temperature commonly associated with other silver bearing minerals. They can be also found in mineral veins and usually formed in low temperature hydrothermal veins. They are usually known deposited from hot aqueous solutions in fault zones of the crust. These are commonly located near the batholiths, the commonly known large igneous bodies. Argentite as is considered most important ore of silver, which is found in great abundance in sulfide mineral deposits of Kongsberg, Norway and Zacatecas, Mexico. They are reportedly found in large masses in some locality such as in the Comstock Lode, Nevada and also in Guanajuato, Mexico. There are also notable occurrences in types of localities that include Freiberg; Cobalt, Ontario, Canada; Cornwall, England; and other areas in the United States including Aspen and Leadville, Colorado and Butte, Montana. Fine mineral crystals are found in the Harz Mountains in Germany and also in Saxony. There are other major deposits reported that include Chile, Peru, and Bolivia.
