Tetradymite

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.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-grey, and the lustre metallic and brilliant. The mineral is very soft (H = 1.5 - 2) and marks paper. The specific gravity is 7.2 to 7.9.
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(n.)
A telluride of bismuth. It is of a pale steel-gray color and metallic luster, and usually occurs in foliated masses. Called also telluric bismuth.
  

General Information:
 Chemical Formula:
Bi2Te2S
 Composition:
(Molecular Weight = 705.23 gm)
Bismuth 59.27 % Bi
Tellurium 36.19 % Te
Sulfur 4.55 % S 
 Empirical Formula:
Bi2Te2S
 Name Origin:
From the Greek, tetradymos, "fourfold."
Physical Properties:
 Cleavage:
[0001] Perfect
 Color:
steel gray or yellow gray.
 Density:
7.2 - 7.9, Average = 7.55
 Diaphaniety:
Opaque
 Habits:
Lamellar - Thin laminae producing a lamellar structure., Granular - Generally occurs as anhedral to subhedral crystals in matrix., Pseudo Hexagonal - Crystals show a hexagonal outline .
 Hardness:
1.5-2 - Talc-Gypsum
 Luminescence:
None.
 Luster:
Metallic
 Streak:
steel gray
More details...

Eng: tetradymite
Urdu: بسمت کا مرکب ۔ عام طور پر درختوں کے جُھنڈ وغیرہ میں بنتا ہے ۔ بھورے فولادی رنگ کا ہوتا ہے ۔