Magnesite Cryptocrystalline

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

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. 

Sedimentary deposits of cryptocrystalline magnesite occur either in lagoons, salt lakes, or freshwater lakes (lacustrine). The genesis of magnesite in saltwater requires specific conditions for it to occur a reducing alkaline environment, a high concentration of magnesium sulfate, and a concentration... 

Sedimentary deposits of magnesite have been described as having either a biogenic origin or a chemical route via direct precipitation. These deposits are cryptocrystalline in form. Actinomycetes bacteria, which belong to the genus Streptomyces, are thought to have played a role in the formation of... 

Deposits of massive cryptocrystalline magnesite occur in serpentized ultra-basic rock that has undergone a hydrothermal leaching of magnesium from the serpentine see reaction (2.5). The hydrothermal solution... 

Magnesite may also form through the serpentization of ultrabasic rock, under low-temperature and low-pressure conditions, which favor the exosolution of hydrothermal cryptocrystalline magnesite. Reaction (2.6) shows serpentization of olivine, (Mg, Fe)2Si04, to form antigorite, H4(Mg, Fe)2Si209, and magnesite ... 

Figure 2.7 Photograph of a cryptocrystalline magnesite nodule. Note the distinguishing conchoidal fracture pattern.

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. 

Magnesite occurs in nature in two distinct textures macrocrystalline and cryptocrystalline. When high-purity, macrocrystalline magnesite, as found in... 

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