Sedimentary Rocks

• Carbonatic Rocks
• Evaporite rocks
• Terrigenous Rocks
Grain Size
Terrigenous Rocks
Packing
Roundness
Sorting

• Weathering

Turbidite

• Turbidites

Fossils

• Ammonites
• Bivalves
• Brachiopods
• Gastropods
• Trilobites

Sedimentary Minerals

• Anhydrite
• Baryte
• Chalcedony
• Gypsum
• Glauconite
• Magnesite

Texture

• Allochem
• Carbonatic Matrix
• Dolomitization
• Syntaxial Overgrowthn

Rocks

• Ammonitico Rosso
• Arkosic Sandstones
• Bioclastic Grainstone
• Oolitic Ironstone
• Breccia
• Conglomerate
• Encrinite
• Lithic Arenite
• Mudstone
• Oolite
• Orthoconglomerate
• Radiolarite
• Wackestone

Magnesite - MgCO₃

Magnesite is a mineral with the chemical formula MgCO₃. It occupies one end of a solid solution series with siderite (FeCO₃), as the iron ion Fe²⁺ substitutes for the magnesium ion Mg²⁺. Calcium, manganese, cobalt and nickel may also occur in small amounts.

Magnesite occurs as veins in and an alteration product of ultramafic rocks, serpentinite and other magnesium rich rock types in both contact and regionalmetamorphic terrains. These magnesites often are cryptocrystalline and contain silica in the form of opal or chert.

Magnesite is also present within the regolith above ultramafic rocks as a secondary carbonate within soil and subsoil, where it is deposited as a consequence of dissolution of magnesium-bearing minerals by carbon dioxide within groundwaters. Magnesite can be formed via talc carbonate metasomatism of peridotite and other ultrabasic rocks. Magnesite is formed via carbonation of olivine in the presence of water and carbon dioxide at elevated temperatures and high pressures typical of the greenschist facies.

Magnesite can also be formed via the carbonation of magnesium serpentine (lizardite) via the following reaction:

2Mg₃ Si₂O₅(OH)₄ + 3CO₂ → Mg₃Si₄O₁₀(OH)₂ + 3MgCO₃ + H₂O (serpentine + carbon dioxide → talc + magnesite + water)

Optical Properties:

• Color: Colorless, White, Grayish white, Yellowish white, Brownish white.
• Habit: Massive - Fibrous - Distinctly fibrous fine-grained forms.

Bibliography

• Deer, W.A., Howie, R.A., Zussman, J. (1998) Rock-forming Minerals.
• Optical Mineralogy : The Nonopaque Minerals by Phillips / Griffen
• E. WM. Heinrich (1956): Microscopic Petrografy. Mcgraw-hill book company,inc

Photo

Colorless Magnesite crystals. PPL image, 2x (Field of view = 7mm)	Magnesite crystals. XPL image, 2x (Field of view = 7mm)	Magnesite crystals. XPL image, 2x (Field of view = 7mm)
Magnesite crystals. XPL image, 2x (Field of view = 7mm)	Magnesite crystals. XPL image, 2x (Field of view = 7mm)	Magnesite crystals. XPL image, 2x (Field of view = 7mm)
Magnesite crystals. XPL image, 2x (Field of view = 7mm)