Magnesite Crystalline

Texture. All limestones are crystalline, but there is tremendous variance in the size, uniformity, and arrangement of their crystal lattices. The crystals of the minerals calcite, magnesite, and dolomite are rhombohedral those of aragonite are orthorhombic. The crystals of chalk and of most quick and hydrated limes are so minute that these products appear amorphous, but high powered microscopy proves them to be cryptocrystalline. Hydrated lime is invariably a white, fluffy powder of micrometer and submicrometer particle size. Commercial quicklime is used in lump, pebble, ground, and pulverized forms. 

SiNHA, P.A. ETAL 1989. Crystalline magnesite associated with Vempalle dolomites of Cuddapah Basin, Andhra Pradesh. Journal -Geological Society of India, 33, 183-185. 

In several reports, the severity of the pneumoconioses caused by the action of magnesite ore dusts was found to be a function of the crystalline silica content. ... 

Adverse health effects have not been reported for workers exposed to magnesite containing no asbestos and <1% crystalline silica. No cases of human systemic magnesium intoxication from inhalation of magnesite have been reported. 

The 2003 ACGIH threshold limit value-time-weighted average (TLV-TWA) for magnesite is 10mg/m total dust containing no asbestos and <1% crystalline silica. 

Vleesschauwer (1970) prepared two series of mesoporous batches of MgO by the heat treatment of crystalline MgCOj (magnesite) and crystalline MgC03.3H20 (nesquehonite). A maximum surface area of about 350 m2 g 1 was obtained by calcination of the latter precursor at 400°C. Although the thermal decomposition of magnesite resulted in the development of lower surface areas (< 140 m2 g 1) the products appeared to have a more uniform mesopore structure. Thus, the nitrogen isotherm determined on a sample calcined for 24 hours at 800°C exhibited a narrow, almost vertical, hysteresis loop at p/p° 0.9. 

Crypto-crystalline (compact) magnesites with a low content of iron oxides. They are used in the manufacture of caustic magnesia (i.e. low-fired active MgO for the chemical industry, for the manufacture of oxychloride cements, etc.). When calcined at suitably high temperatures, they serve as an excellent raw material for the manufacture of refractories. 

There are two physical forms of magnesite cryptocrystalline or amorphous magnesite and crystalline, macrocrystalline, or bone magnesite. 

In the Almora area of Uttar Pradesh State, coarsely crystalline magnesite occurs in association with dolomite, talc, cherty limestone, and... 

A cryptocrystalline magnesite deposit was discovered in 1962 near Zarghat in the Hijaz Mountains. Although relatively pure, the deposit is small. Another crystalline, high-lime silica magnesite deposit was also discovered in 1962 at Jabal A1 Rokhan, which is located about 59 km northeast of Mahd adh Dhahab. Both of these deposits are being evaluated for possible exploitation. 

Hardness 3.5-4.5 on the Mohs hardness scale. Crystalline magnesite tends to be softer than the cryptocrystalline variety. 

CHRONIC HEALTH RISKS substances may have effects on the lungs if the magnesite contains more than 1% crystalline silica. 

Classification Crystalline salt Definition Basic dehydrated magnesium carbonate or normal hydrated magnesium carbonate the naturally occurring mineral is magnesite Empirical CO3 Mg... 

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