Tetradymite

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Tetradymite
Tetradymite.jpg
Tetradymite - British Columbia, Canada
General
CategorySulfide mineral
Formula
(repeating unit)
Bi2Te2S
Strunz classification2.DC.05c
Dana classification02.11.07.01
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3m)
H-M symbol: (3 2/m)
Space groupR3m
Identification
ColorSteel-gray with dull to iridescent tarnish; white in polished section
Crystal habitPyramidal prisms, commonly granular, massive to foliated, also bladed
TwinningTwin planes {0118} and {0115}
CleavagePerfect on {0001}
FractureUneven
TenacityLaminae flexible, slightly sectile.
Mohs scale hardness1.5 - 2
LusterMetallic, splendent on fresh surfaces, dull if tarnished
StreakSteel-gray
DiaphaneityOpaque
Specific gravity7.2 - 7.9
References[1][2][3][4]

Tetradymite is a mineral consisting of bismuth, tellurium and sulfide, Bi2Te2S, also known as telluric bismuth. If sulfur is absent the mineral is tellurobismuthite and the formula is then Bi2Te3. Traces of selenium are usually present.

A sample of tetradymite

Crystals are rhombohedral, but are rarely distinctly developed; they are twinned together in groups of four; hence the name of the mineral, from the Greek for fourfold. There is a perfect cleavage parallel to the basal plane and the mineral usually occurs in foliated masses of irregular outline. The color is steel-gray, and the luster metallic and brilliant. The mineral is very soft (H = 1.5 - 2) and marks paper. The specific gravity is 7.2 to 7.9.

The type locality is Zupkov (Zsubko; Schubkau), Stredoslovenský Kraj, Slovak Republic where it was reported in 1831.[4] It was first found, in 1815, at Telemark in Norway. It often occurs in high temperature hydrothermal quartz veins associated with native gold and in contact metamorphic deposits.[2]

References[edit]

Attribution
  •  This article incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). "Tetradymite". Encyclopædia Britannica (11th ed.). Cambridge University Press.

External links[edit]