Madocite

Madocite
General
Category Sulfosalt mineral
Formula
(repeating unit)		 Pb17(Sb,As)16S41
Strunz classification 02.LB.30
Crystal symmetry Orthorhombic pyramidal
H-M symbol: mm2
Space group: Pb2a
Unit cell a = 27.2 Å, b = 34.1 Å,
c = 4.06 Å; Z = 2
Identification
Color Grayish black
Crystal habit Elongated and striated crystals; massive
Crystal system Orthorhombic
Cleavage {010} Perfect
Fracture Conchoidal
Mohs scale hardness 3.25
Luster Metallic
Streak Grayish black, shining
Diaphaneity Opaque
Specific gravity 5.98
Pleochroism Strong, from white to gray
References [1][2][3][4]

Madocite is a mineral with a general formula of Pb17(Sb,As)16S41. Madocite was named for the locality of discovery, Madoc, Ontario, Canada. It is found in the marbles of the Precambrian Grenville Limestone.[4] It is orthorhombic (rectangular prism with a rectangular base) and in the point group mm2. Its crystals are elongated and striated along [001] to a size of 1.5 mm.

Madocite is anisotropic and classified as having high relief. It also displays strong pleochroism.[3]

Madocite is found in small clusters in marble pits (near Madoc, Ontario), and was originally categorized in the 1920s as an unidentified sulfosalt mineral in an assemblage of pyrite, sphalerite, and jamesonite in marble. Later research was done by John L. Jambor in the 1960s who went to the site and collected samples of the assemblages.[5]

References

  1. ↑ Mindat.org
  2. ↑ (1968) American Mineralogist, 53, 1421
  3. 1 2 Webmineral data
  4. 1 2 Anthony, J. W., Bideaux, R. A., Bladh, K. W., and Nichols, M. C. (1990) Handbook of Mineralogy: Volume 1: Elements, Sulfides, Sulfosalts. 306 p. http://rruff.geo.arizona.edu/doclib/hom/madocite.pdf
  5. ↑ History of discovery


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