magnesite on dendritic quartz


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an unusual specimen of magnesite dendritic quartz sometimes named bitter spar

Mineral Group  carbonate + oxide
Composition  MgCO3, SiO2
dimension (cm)  6x4x3
weight (g)  107

The most common form of Magnesite is white, microcrystalline, porous masses that are dull in luster, and have the appearance of unglazed porcelain. Because they are porous, they adhere to the tongue when licked.

An interesting Magnesite occurrence is in Brumado, Brazil, where a deposit of clear, well formed, rhombohedrons similar to Iceland Spar Calcite found. Until this find, such crystals were, although identical in appearance to Iceland Spar Calcite, they are much rarer and sought after. Common Iceland Spar Calcite has been wrongly labeled by some unscrupulous dealers as Magnesite to stimulate sales.

Magnesite belongs to the calcite group of minerals, a group of related carbonates that are isomorphous with one another. They are similar in many physical properties, and may partially or fully replace one another, forming a solid solution series. All members of the calcite group crystallize in the trigonal system, have perfect rhombohedral cleavage, and exhibit strong double refraction in transparent rhombohedrons.

This variety of quartz is termed “dendritic” due to its internal collection of dendrites. Dendrites are fern-like inclusions of iron, manganese, or other metallic oxides see Wikipedia

Additional information

Weight 107 g
Dimensions 6 x 4 x 3 cm