Siderite

Physical Properties
Chemical formula FeCO3
Class Carbonate
Crystal system Hexagonal (rhombohedral)
Habit Typically rhombohedra, often with
curved faces
Fine- to coarse-grained aggregates
Colloform
Globular
Botryoidal
Fibrous
Earthy
Color Light to dark brown
Hardness 3.5 to 4
Specific gravity 3.96
Cleavage Perfect rhombohedral {101}
Fracture Subconchoidal
Luster Vitreous
Transparency Translucent
Streak White
Optical Properties
PPL Typically colorless to pale
yellow-brown
XPL High 2nd to low 3rd order colors
δ 0.242
Special properties Effervesces in warm HCl
after Perkins, 383

Siderite Hand Sample

Siderite in hand sample

Siderite in Thin Section

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Further Reading

Siderite at webmineral.com

Siderate at mindat.org