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Platte Canyon High School
Bailey, Colorado

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The Alma King

Crystallography:  Hexagonal.  Occurs rarely as rhombohedral crystals.  Usually occurs as massive and granular.

Physical Properties:  Cleavage {1011} perfect; Hardness 3.5-4; Luster vitreous.  Color usually some shade of rose-red; may be light pink to dark brown.  Streak is white.  Opacity transparent to translucent.

Composition:  End member of a solid solution series from rhodochrosite (MnCO3) to siderite (FeCO3); also some substitution of Mn2+ with Ca2+ (kutnahorite - CaMn(CO3)2)

Diagnostic Features:  Characterized by color and cleavage.  Hardness distinguishes it from rhodonite (MnSiO3). 

Occurrence:  Occurs in hydrothermal veins with ores of silver, lead, and copper.  The finest crystals come from the Sweet Home mine near Alma, Park County, Colorado.  Also found at Alicante, Lake County and elsewhere in Colorado.  Banded rhodochrosite is mined in Argentina.


The Alma King
  Reference: Klein and Hurlbut, Manual of Mineralogy, 1985