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argentite

 
Dictionary: ar·gen·tite   (är'jən-tīt') pronunciation
n.
A valuable silver ore, Ag2S, with a lead-gray color and metallic luster that is often tarnished a dull black.


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Chemistry Dictionary: argentite
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A sulphide ore of silver, Ag2S. It crystallizes in the cubic system but most commonly occurs in massive form. It is dull grey-black in colour but bright when first cut and occurs in veins associated with other silver minerals. Important deposits occur in Mexico, Peru, Chile, Bolivia, and Norway.



Rock & Mineral Guide: argentite
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Ag
Cubic -- hexoctahedral

Environment

In fairly low-temperature ore veins formed at some distance from the primary source.

Crystal description

Frequently occurs in poorly formed, dull black crystals, usually cubic but often so distorted and branching that it is difficult to recognize their faces. Commonly massive.

Physical properties

Dark lead gray. Luster metallic, usually tarnished to dull black; hardness 2-2Ɖ; specific gravity 7.3; fracture subconchoidal; cleavage poor cubic and dodecahedral. Like lead, can be cut by a knife (sectile).

Composition

Silver sulfide (87.1% Ag, 12.9% S).

Tests

Blowpipe fuses it into a bead on charcoal, which in an oxidizing flame gives silver button. Tests for silver then apply.

Distinguishing characteristics

Sectility distinguishes it from other sulfides, particularly galena (which shows far better brittle cleavage). Grayer color distinguishes it from very white native silver; colorless nitric acid solution distinguishes it from chalcocite; copper nitrate solution is green.

Occurrence

Argentite is the most important primary ore of silver. Of common occurrence in veins with native silver. It seems to have catalytic power, with wire silver appearing to rise from argentite crystal surfaces. Fine crystals are found in Mexico, in Saxony, at Kongsberg, Norway, and at Cobalt, Ontario. Encountered near the surface of ore veins; there are no good commercial occurrences remaining in the U.S.

Remarks

Argentite has a cubic structure only at temperatures above 180°C, so its presence indicates that the vein formed at temperatures higher than 180°C. Actually all Ag 2 S specimens are structurally rearranged into acanthite (orthorhombic Ag 2 S) at room temperature and are now pseudomorphs after the original cubic argentite.



WordNet: argentite
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Note: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: a valuable silver ore consisting of silver sulfide (Ag2S)


Wikipedia: Argentite
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Argentite sample
The unit cell of argentite

Argentite was primarily treated as a mineral belonging to the galena group, cubic silver sulfide (Ag2S), occasionally found as uneven cubes and octahedra, but more often as dendritic or earthy masses, with a blackish lead-grey color and metallic lustre. All these forms are structurally not argentite, but its monoclinic polymorph, acanthite. Due to instability in normal air temperature, the IMA commission decided to reject this mineral, which now is a discredited mineral species. The cubic cleavage, which is so prominent a feature in galena, here present only in traces. The mineral is perfectly sectile and has a shining streak; hardness 2.5, specific gravity 7.3. It occurs in mineral veins, and when found in large masses, as in is Mexico and in the Comstock Lode in Nevada, it forms an important ore of silver. The mineral was mentioned 1529 by G. Agricola, but the name argentite (from the Lat. argentum, silver) was not used till 1845 and is due to W. Haidinger. Old names for the species are Glaserz, silver-glance and vitreous silver. A related Cu-rich mineral occurring i.e. in Jalpa, Mexico, is known as jalpaite.

Acanthite, also Ag2S, crystallizes in the monoclinic system and is the stable form below 177oC. As argentite cools below that temperature its cubic form is distorted to the monclinic form of acanthite. Thus, only acanthite is stable in normal air temperature and only this form is naturally found.

References


 
 
Learn More
aguilarite (mineralogy)
Acanthite (mineralogy and petrology)
silver

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Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
Chemistry Dictionary. A Dictionary of Chemistry. Sixth Edition. Copyright © Market House Books Ltd, 2008. All rights reserved.  Read more
Rock & Mineral Guide. Peterson Field Guide to Rocks and Minerals, by Frederick H. Pough. Copyright © 1998 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.  Read more
WordNet. WordNet 1.7.1 Copyright © 2001 by Princeton University. All rights reserved.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Argentite" Read more