Mineral description : Magnesite

Picture pending, magnesite from Horstmannaho, Autokumpu area, Finland.
Magnesite crystal from Altemark, Mo i Rana, Norge.
Hard to see, covered in chlorite, but it's half the piece.

Mineral class Carbonates : calcite group
Chemical formula MgCO3
Crystal system Trigonal
Habitus Often massive or grainy. Crystals rhomoedric or prismatic.
Cleavage Romboedric, complete.
Hardness 3.5-4.5
Density 3.0-3.2 (rising with iron content)
Color Usually colorless or white when pure, gray yellow or brownish nuances when iron is present.
Streak White
Luster Glas to pearly.
Description Used as base for making cement and fireproof bricks.
Occurance Magnesite is less common than calcite and is rarely created as sedimentary rock.
It often occurs as metasomatic altered rocks, in magnesium rich rock altered by carbonate rich solutions, or carbonatic rock altered by magnesium rich solutions.
Associates Talc and serpentinites.
Notes Magnesite looks like calcite but is almost not affected by cold hydrochloric acid. Reacts strongly with hot hydrochloric acid.
Breunnerite is a name on a magnesite with 5-30% iron
Locations Magnesite have been mined in some places along the fjelds.
  • Tarrekaise, northern Lappland.
  • Äpartjåkko, northern Lappland.
Also common in talc around peridotites.
  • Laisholm, Hemavan. As light brown crystals in talc.
  • Horstmannaho, Finland. As light yellow crystals in talc.
  • Altemark, Norway. In talc and chlorite around a peridotite.

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Mineral group index.
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Last changed : 1998-03-07