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Formula: Ag
Native element, transition metal
Varieties
Küstelite is a variety of silver containing 10% - 30% of gold
Antimonial silver is a variety of silver containing less than 5% of
antimony
Native amalgam is a mercury-bearing variety of silver
Properties of Silver
Crystal System: Isometric
Specific gravity: 10.1.to 11.1 measured, 10.497 calculated
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).
Silver from the Langis Mine - Image
At the Yueshan Ag-Pb-Zn deposit, Huangtun township, Lujiang County, Hefei, Anhui, China, silver is found as "wire silver"
(AESS).
Silver from Yueshan - Image
At the Lin Ma Hang mine, North District, New Territories, Hong Kong, China, the
lead-zinc deposit is a hydrothermal
deposit which lies along a fault zone within altered acid volcanic rocks, consisting mainly of
chlorite, biotite,
sericite and actinolite, with
scattered quartz.
(Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)
The mineralisation consists of a series of fissure vein deposits varying from a few mm to several metres on width. The
initial vein filling was coarse milky quartz. this was followed by an intrusion
of fine-grained quartz carrying the metallic minerals,
galena, pyrite,
sphalerite and chalcopyrite,
in order of abundance
(Geological Society of Hong Kong Newsletter, 9.4.3-27).
Silver-bearing galena occurs as
cleaveable granular masses
(Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council).
At Chuen Lung, Tsuen Wan District, New Territories, Hong Kong, China, in fissure veins in
granite rocks in a small stream near Chuen Lung,
silver-bearing galena occurs associated
with massive granular amber coloured sphalerite,
chalcopyrite,
pyrite and pyrrhotite
(Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)
The Lin Fa Shan deposit, Tsuen Wan District, New Territories, Hong Kong, China, is located in a remote area of the Tai Mo Shan
Country Park, on a steep west facing slope of Lin Fa Shan, just above the abandoned village of Sheung Tong. The
surrounding hillsides are covered with shallow excavations, representing past searches for
wolframite, the natural ore of
tungsten. The abandoned workings are extremely dangerous with unsupported tunnels, open shafts and no maintenance since
their closures in 1957; the workings should not be entered
(http://industrialhistoryhk.org/lin-shan).
Silver-bearing galena occurs here
(Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council).
The Bairendaba Ag-polymetallic deposit, Hexigten Banner, Chifeng City, Inner Mongolia, China, is a mesothermal
magmatic-hydrothermal vein-type silver -
lead - zinc deposit, hosted in
Hercynian (about 419 to 299 million years ago) quartz
diorite.
It is suggested that, with decreasing temperature, mineral compositions changed progressively from
tungstate and oxide, to diatomic sulphide, to simple sulphide, to an
antimony sulphosalt mineral, and finally to an
antimonide.
The sequence of visible silver mineral deposition goes from
tetrahedrite (sic) to
freibergite, diaphorite,
freieslebenite,
pyrargyrite and dyscrasite.
In addition, silver atoms occur within the lattices of
chalcopyrite, bornite,
chalcocite, pyrite and
galena
(Minrec 53.347-359).
At the Příbram District, Central Bohemian Region, Czech Republic, silver has been found as
pseudomorphs after dyscrasite
(KL p117).
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).
Silver from Tsumeb - Image
At the Clargillhead vein, Garrigill, Alston Moor, Eden, Cumbria, England, UK, native silver occurs both as
1 to 2 micron diameter ‘droplets’ within banded limonite which locally
forms alteration crusts on chalcopyrite and rarely as discrete
grains up 8 microns within the
quartz-fluorite
gangue
(JRS 23.51).
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).
Silver from the New Cliffe Hill Quarry - Image
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).
Silver from the Magma Mine - Image
At Keweenaw county, Michigan, USA, some fine silver specimens have been found. They include crystallised
silver 9.4 cm wide on a little prehnite matrix from near the North Cliff
mine, a lone 1.9 mm wide twinned silver crystal on a crystallised
pumpellyite substrate from the Franklin mine, and a striking specimen of
ropy copper partially encrusted with blobs of silver from the Isle Royale
mine
(R&M 97.4.354-363).
The Central Mine, Central, Keweenaw county, Michigan, USA, initially targeted a series of sub-parallel mineralised
fissure veins where the most copper-rich portion of the vein was close to the
base of the main greenstone flow.
The Central mine has produced some outstanding examples of crystallised silver, typically showing branching
arborescent crystallisation, composed of complexly twinned tetrahexahedral and
spinel-twinned forms. Specimens showing native silver on native
copper, and rarely the reverse, are known from the Central mine as well.
Crystallised silver specimens are sometimes associated with prehnite,
quartz, epidote and other minerals
(MinRec 54.1.81).
Silver from the Central Mine - Image
At the Copper Falls Mine, Copper Falls, Keweenaw county, Michigan, USA, mineralisation occurs primarily in hydrothermal veins
cutting preexisting lavas and as amygdules in the Ashbed flow.
Despite records of significant amounts of silver being recovered, mostly from the veins, very few silver specimens
from the mine survive. Most of the known silver specimens were discovered in 1980 in a small surface-exposed vein which
had never been mined. Silver specimens from this find consist of delicately branching groups of hoppered crystals, mostly
cubes. Most of the crystals are quite small, few exceeding 5 mm, yet the specimens are exquisite and highly sought after
(MinRec 54.1.112-113).
Silver from the Copper Falls Mine - Image
The Cliff Mine, Phoenix, Keweenaw county, Michigan, USA, is situated at the base of a roughly 70-metre
basalt cliff. A curious feature of the impressive thickness of the
greenstone flow here is that it contains zones of “pegmatoid”: areas
where
slow cooling in the core of the lava flow allowed for large feldspar crystals
exceeding 1 cm to grow. Such features are normally only observed in intrusive igneous rocks and are almost unheard of
in basalt flows.
The Cliff mine primarily exploited rich copper mineralisation in the Cliff
fissure (vein). Although mineralised with copper to some extent along its
entire length, the part of the vein just below the greenstone flow
carried the richest copper mineralisation by far. A significant amount of the
copper recovered at the Cliff mine came from amygdaloids in the tops of 13
basalt flows which were cut by the Cliff vein. The discovery and mining
of this vein proved that the veins were the source of the large masses of float
copper that were already well known, and proved that the
primary ore mineral in the district was native
copper, not sulphides, as had been suspected earlier.
The Cliff vein is widely regarded as one of the most silver-rich in the Lake Superior District. Cliff mine
silver specimens are typically made up of complex twinned crystals, often severely distorted. Wires and sheets
of silver have also been found in the Cliff mine
(MinRec 54.1.25-49).
Silver from the Cliff Mine - Image
At the Tintic Mining District, Utah, USA, In the Tintic District, silver generally occurs where there is
galena, chiefly as small sheets or wires up to a centimeter or two in
length. Secondary wires of silver were found at the
Gemini mine, below the water table. On one of the specimens, a wire of silver was found penetrating a crystal
of cerussite. Silver has also been found where
tellurium is abundant, in sheets and wires only a millimeter or two in
size, with tellurides of silver and
gold
(MinRec 55,2,221).
Silver from Tintic - Image
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
argentopentlandite
argentopyrite
arsenopyrite
canfieldite
kravtsovite
mckinstryite
panskyite
petrovskaite
pirquitasite
sternbergite
stromeyerite
uytenbogaardtite
Tellurides
hessite
krennerite
petzite
sopcheite
sylvanite
volynskite
Sulphosalts
argentotennantite
baumstarkite
benjaminite
cupropavonite
écrinsite
ferrofettelite
fizelyite
freieslebenite
gustavite
hatchite
jasrouxite
kenoargentotetrahedrite-(Fe)
makovickyite
miargyrite
ourayite
owyheeite
pearceite
polybasite
proustite
pyradoketosite
pyrargyrite
sicherite
stephanite
thunderbayite
treasurite
trechmannite
vikingite
xanthoconite
Halides
bideauxite
bromargyrite
chlorargyrite
iodargyrite
Sulphates
argentojarosite
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