Mineral Information and Data:

Siderite
FeCO3 [CNMNC approved formula]

Named from the Greek sideros = iron.

IMA status : Approved Species 1845 ()
CLASSIFICATION 
Dana
(8th edition) :
14.01.01.03  
  (14) Anhydrous Carbonates
  (14.01) with Simple Formula A+ CO3
  (14.01.01) Calcite Group (Trigonal: R-3c)
  
Nickel-Strunz
(10th edition) :
05.AB.05
  (05) Carbonates and Nitrates
  (05.A) Carbonates without additional anions, without H2O
  (05.AB) Alkali-earth (and other M2+) carbonates
  
Crystal system: Trigonal System
Point group (H-M): 3m (or 3 2/m) — hexagonal-scalenohedral
Unit cell: a = 4.69 Å, c = 15.39 Å
Crystal Habit: Crystals rhombohedral or tabular, prismatic, scalenohedral, massive, coarse to fine granular, botroydal, globular
Twinning: Uncommon on {01-12} lamellar, uncommon on {0001} simple
  
Color: Pale yellowish, pale green, yellowish brown, brown, reddish
Diaphaneity: Translucent
Luster: Vitreous, may be pearly or silky
Hardness (Mohs): 3.5 - 4.5
Measured Density: 3.96 g/cm3
Cleavage: 1; {1011} perfect
Tenacity: Brittle
Fracture: Uneven to conchoidal
Streak: White
  
Polymorphism and Series: Forms three series, with magnesite, with rhodochrosite, and with smithsonite.
Geologic Setting: A common component of bedded sedimentary iron ores and metamorphic iron formations; in hydrothermal metallic veins; rarely in granite and nepheline syenite pegmatites; in carbonatites; authigenic, and in concretions.
Mineral Association: Quartz, barite, fluorite, pyrite
  
Synonyms/varieties: Chalybite, oligonite (Mn-rich variety), sphaerosiderite (spherically-aggregated variety)
Other Properties: Pyromagnetic (ferromagnetic after heating). BioMineral.

 

Siderite
Transparent, amber brown siderite rhombs to 6 mm with light green brazilianite crystals to 2 mm
Origin: Stoneman Camp, Rapid Creek, Yukon, Canada
Sample size: 5 x 3 x 2 cm
Photo: Tom Loomis

 

Siderite
(zoom-in of above)

 

Siderite
Siderite with quartz
Origin: Galena Mine, Wallace, Shoshone Co., Idaho, United States
Sample size: 5 x 4.5 x 3 cm
Photo: Tom Loomis

 

Siderite
(zoom-in of above)

 

Siderite
Siderite and barite (white/colourless)
Origin: Frostburg, Allegany Co., Maryland, U.S.A.
Sample size: Microscopic image
Photo and Owner: Lou Perloff

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