Siderite

Siderite takes its name from the Greek word "sideros" - iron, reflecting its iron content.

The colour ranges from yellow to dark brown and sometimes black, which is caused by presence of manganese (sometimes called manganosiderite).

Transparent crystals are cut into attractive faceted gems for collectors. Massive material is cut as cabochons.

Fine crystal specimens come from Bohemia, Cornwall (England), France, Germany, Switzerland. Amber-coloured gem-quality crystals of Siderite were recovered from Tsumeb copper mine, Northern Namibia.
General Information
Chemical Formula
Fe
2+
 
CO
 
3
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Photos of natural/un-cut material from mindat.org
Physical Properties of Siderite
Mohs Hardness3.5 to 4.5
Walter Schumann, Gemstones of the world (2001)
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Specific Gravity3.83 to 3.89
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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TenacityBrittle
Anthony et al, Handbook of mineralogy (2001)
Cleavage QualityPerfect
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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FractureUneven
Arthur Thomas, Gemstones (2009)
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Optical Properties of Siderite
Refractive Index1.633 to 1.875
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Optical CharacterUniaxial/-
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Birefringence0.240
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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PleochroismNil
Arthur Thomas, Gemstones (2009)
DispersionStrong
Arthur Thomas, Gemstones (2009)
Colour
Colour (General)White, yellowish-white, yellow, brown
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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TransparencyTransparent,Translucent,Opaque
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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LustreVitreous
Arthur Thomas, Gemstones (2009)
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Crystallography of Siderite
Crystal SystemTrigonal
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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HabitRhombohedral to steep scalenohedral
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Geological Environment
Where found:Siderite occurs in sedimentary deposits and hydrothermal ore veins.
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Further Information
Mineral information:Siderite information at mindat.org
Significant Gem Localities
Brazil
 
  • Minas Gerais
    • Nova Lima
Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 451
Namibia
 
  • Oshikoto Region
    • Tsumeb
Peru
 
  • Junín
    • Yauli Province
      • San Cristobal District
Portugal
 
  • Castelo Branco
    • Covilhã
Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 451
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