Ankerite

Formula:  Ca (Fe, Mg, Mn)(CO₃)₂

Origin of name:  For Mathias Joseph Anker (1771-1843), Austrian mineralogist

Crystal system:  Hexagonal

Crystal class:  -3

Twinning:  Common on {0001}, {10-10}, or {11-20}

Unit cell:   a = 4.82 Å, c = 16.13 Å

Colour:  White, Grey, yellowish brown to brown

Diaphaneity: Translucent to opaque

Luster:  Vitreous to pearly

Habit:  Crystals simple rhombohedrons; massive, fine to coarse granular

Hardness:  3.5 to 4

Specific gravity:  2.97 to 3

Cleavage:  1; {10-11}perfect

Tenacity:

Streak: White

Synonyms/varieties:

Comments:  Series with dolomite and with kutnahorite. Common in ore-bearing rocks as rock-forming mineral (gangue). High Fe contents are observed in ankerite associated with iron ores.