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Proustite Mineral Facts:
Chemical
Formula: AgAsS3 (Light
Ruby Silver)Sulfo-arsenite
of silver, silver is 64.5 % by weight. May
contain a small
amount of antimony substituting for arsenic.
Colors:
Ruby Red to Brownish red
Its color is scarlet in transparent pieces by transmitted light. Under
the long-continued influence of daylight the color deepens until it
becomes darker than that of pyrargyrite. Its streak is deep red to
brownish black.
Hardness:
2.0
Density: 5.5
Cleavage:
Imperfect,
but
it is easily sectile, and can be cut with a knife like lead.
Crystallography: Rhombohedral
Found in
pointed
crystals, but more commonly occurs as granular and massive forms.
Luster:.
Adamantine luster.
Transparent to translucent. High refractive index.
Optics:
(Refractive Index):
w= 3.0877, e= 2.7924
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Composition,
Structure and Associated Minerals:
Proustite,
or light ruby silver, is isomorphous with
pyrargyrite. It differs from the latter mineral in containing arsenic in
place of antimony. It occurs both massive and in crystals, and like
pyrargyrite is an important silver ore. The mineral occurs in veins
associated with other compounds of silver such as
native silver,
acanthite (argentite),
stephanite,
and sometimes with
galena
and
arsenopyrite. It is most commonly found in the zone of secondary
enrichment of silver veins, but also is formed as a primary ore mineral in
some near surface epithermal systems rich in silver.
Identification and Diagnostics
Characterized
chiefly by its ruby-red color and streak and its brilliant luster. Its
reaction for silver serves to distinguish it from
cuprite,
cinnabar and
realgar, which it sometimes resembles. Proustite differs from
pyrargyrite in its color, transparency and streak, as well as in its arsenic
reactions.
Proustite gives
reactions for arsenic where this mineral reacts for antimony, and yields
only sulphur when dissolved in HNO3. From its solution in KOH a
yellow precipitate of As2S3 is thrown down upon the addition of
HC1 (compare with pyrargyrite).
Occurrence,
Localities and Origins:
Overall, proustite is a fairly
rare mineral, occurring
in silver veins associated
with various other sulpharsenites and sulphantimonites.
It is generally less abundant than
pyrargyrite.
Found in the silver mines of Saxony; Bohemia; at Chaftarcillo, Chile, in
fine crystals; common in the silver mines of Peru and Mexico. Found in
Colorado in the silver mines of the San Juan Mountains and elsewhere; in
various epithermal silver districts in Nevada, etc.
Handsome crystal specimens of
proustite occur at Freiberg and other places in Saxony, at Wolfach in Baden,
at Markirchen in Alsace and at Chanarcillo in Chile. It is associated with
pyrargyrite and with other ores of silver. In parts of the western United
States it is quite abundant, more particularly
in the Ruby district, Colorado,
at Poorman lode in Idaho, and in all other localities where pyrargyrite
occurs. In
some locations it is an important
silver ore.
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