Silicates: Forsterite
Diagnostic card.
Mg 2 SiO 4
Diamond orthogonality
Hardness 6-7
Specific weight 3,2-3,3
Cleavage is easy, distinct
Cracked shell
Color yellow to green
Color in powder white
Glitter glass
In nature it occurs in the form of short-columned crystals, the shape of which is determined by the combination of a vertical prism and a side pinacoid, a rhombic pyramid and a basal pinacoid.
In addition, the mineral appears in the form of irregular grains. Color may be absent or vary from yellow to pale green. Forsterite has a glass shine and a conchoidal fracture. Forms an isomorphic series with fayalite, which is called olivine . Yellow, olive green, colorless, light gray color.
Chemical composition. Magnesium oxide (MgO) 57.1%, silica (SiO2) 42.9%. Class of symmetry. Rhombo - bipyramidal - mmm. Form of crystalline precipitates. Granular aggregates, dense masses. Cleavage. Clear by (010).
Diagnostic signs.
Does not melt in the flame of a candle and does not lend itself to the action of hydrochloric acid. Triturated into powder, under the action of concentrated sulfuric acid, releases jelly-like silica. Dissolves in sulfuric acid to form a gelatinous silica precipitate.
Origin.
The genesis of the mineral is due to magmatic crystallization; Less often it is associated with contact metamorphism.
Place of Birth.
Forsterite, almost devoid of impurities, is rare on the surface of the earth. It is represented in serpentinites of Sharum in Norway, in small crystals with many facets in geodes among the outcrops of the volcano Monte Somma (in Vesuvius) and in Lazio. Forsterite is found in granular limestone in Bolton (Massachusetts, USA), where it was renamed boltonite .
Forsterite. Spinning nodules (15 cm), folded by a granular aggregate of forsterite, pyroxene, chromium-diopside and others. From basaltic lava. Canary Islands, Atlantic Ocean; Spain. Forsterite (different peridot), magnetite. Naran-Kagan Valley, Pakistan. Munich show-2007.
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