Silver

silver

bornite

zeolite

chalcocite

Images

Formula: Ag
Native element, transition metal

Varieties

Küstelite is a variety of silver containing 10% - 30% of gold

Properties of Silver

Specific gravity: 9.6 - 12
Hardness: 2½ to 3
Streak: Silver white
Colour: Silver white
Solubility: Insoluble in hydrochloric acid; slightly soluble in sulphuric acid; moderately soluble in nitric acid
Melting point: 961.95oC
Boiling point: 2155V
Abundance: 75 parts per billion by mass, 20 parts per billion by moles in the Earth's crust, 1 part per billion by mass, 10 parts per trillion by moles in the Solar System (ChC)
Common impurities: Au,Hg,Cu,Sb,Bi
Environments:

Plutonic igneous environments
Placers
Hydrothermal environments

Native silver is found in the enriched zone of hypothermal (high temperature) hydrothermal veins, and sometimes also as a primary mineral, either in epithermal (low temperature) veins associated with sulphides, zeolites, calcite, baryte, fluorite and quartz, or in hypothermal (high temperature) veins associated with uraninite, arsenides and sulphides of cobalt, nickel and silver and native bismuth.

Localities

At the Mount Kelly deposit, Gunpowder District, Queensland, Australia, the deposit has been mined for oxide and supergene copper ores, predominantly malachite, azurite and chrysocolla. The ores overlie primary zone mineralisation consisting of quartz-dolomite-sulphide veins hosted in dolomite-bearing siltstone and graphitic schist.
Filaments of native silver to 2 mm long were observed with goethite and brochantite on one specimen (AJM 22.1.20).

At Cobalt, Ontario, Canada, skutterudite has been found as pseudomorphs after silver (KL p133).

At the Langis mine, Cobalt, Ontario, Canada, safflorite has been found as pseudomorphs after silver (KL p134).

At the Příbram District, Central Bohemian Region, Czech Republic, silver has been found as pseudomorphs after dyscrasite (KL p117).

At Zacatecas, Mexico, silver has been found as pseudomorphs after pyrargyrite (KL p118).

At Tsumeb, Namibia, native silver has been found associated with chalcocite, and as cementation on native copper (R&M 93.6.548).

At the New Cliffe Hill quarry, Stanton under Bardon, Leicestershire, England, UK, native silver has been found with azurite and cuprite on diorite (RES p198).

At the Magma mine, Pioneer District, Pinal county, Arizona, USA, silver has been found as veinlets and sheets within solid bornite (R&M 95.1.87).

Alteration

Oxidation of pyrite forms ferrous (divalent) sulphate and sulphuric acid:
pyrite + oxygen + H2O → ferric sulphate + sulphuric acid
FeS2 + 7O + H2O → FeSO4 + H2SO4

The ferrous (divalent) sulphate readily oxidizes to ferric (trivalent) sulphate and ferric hydroxide:
ferrous sulphate + oxygen + H2O → ferric sulphate + ferric hydroxide
6FeSO4 + 3O + 3H2O → 2Fe2(SO4)3 + 2Fe(OH)3

Ferric sulphate is a strong oxidizing agent; it attacks silver according to the reaction:

silver + ferric sulphate → silver sulphate + ferrous sulphate
2Ag + Fe2(SO4)3 → Ag2SO4 + 2FeSO4
(AMU b3-3.7)

Silver-bearing minerals include:

Antimonides
allargentum
dyscrasite

Arsenides
kutinaite
novakite

Sulphides
acanthite
aguilarite
argentite
argentopyrite
arsenopyrite
sternbergite
stromeyerite
uytenbogaardtite

Tellurides
hessite
krennerite
petzite
sylvanite
volynskite

Sulphosalts
argentotennantite
baumstarkite
fizelyite
freieslebenite
miargyrite
owyheeite
pearceite
polybasite
proustite
pyrargyrite
stephanite
xanthoconite

Halides
bromargyrite
chlorargyrite
iodargyrite

Sulphates
argentojarosite

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