The mineral magnesite

	Chemical Formula	MgCO₃
	Composition	Magnesium carbonate, commonly with some iron and calcium
	Variable Formula	(Mg,Fe,Ca)CO₃
	Color	Colorless, white, gray, yellowish-brown, flesh
	Streak	White
	Hardness	3½ - 4
	Crystal Forms and Aggregates	(Hexagonal) Magnesite rarely occurs in well formed crystals. When it does, they are rhombohedral crystals, sometimes single but more commonly in groupings and as cleavage fragments. Magnesite also occurs prismatic, but very rarely. The most common form of Magnesite is in massive, compact, porous masses that are dull in luster. Also occurs grainy, coxcomb, and in groups of thin, prismatic needles.
	Transparency	Transparent to nearly opaque
	Specific Gravity	3.0 - 3.3
	Luster	Vitreous to dull
	Cleavage	1,3 - rhombohedral
	Fracture	Conchoidal to even
	Tenacity	Brittle
	Other ID Marks	1) Massive, porous specimens stick to the tongue if licked 2) Occasionally fluorescent (blue and green)
	Varieties	Breunnerite or Ferro-magnesite -Iron rich variety of Magnesite, containing a greater amount of magnesium over iron. Formula = (Mg,Fe)CO₃. If the amount of iron exceeds the magnesium, the mineral is called Sideroplesite, which is a magnesium rich variety of Siderite. Formula = (Fe,Mg)CO₃. Iceland Spar Magnesite - Clear, transparent, Magnesite rhombohedrons that resemble the Iceland Spar variety of Calcite.
	In Group	Carbonates ; Calcite group
	All About	Magnesite belongs to the calcite group, 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 partial solid solution series. All members of the calcite group crystallize in the trigonal subdivision of the hexagonal system (as rhombohedrons and scalenohedrons), have perfect rhombohedral cleavage, and exhibit a strong double refraction in transparent rhombohedrons. 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 has been unearthed in Bahia, Brazil, where a deposit of clear, well formed, rhombohedrons exist. Such crystals have never been found before, and, although identical in appearance to Iceland Spar Calcite, they are much rarer and highly sought after. The common Iceland Spar Calcite is sometimes wrongly labeled by some unscrupulous dealers as Magnesite to stimulate sales.
	Uses	Magnesite is an important ore of magnesium, and used as insulating material.
	Striking Features	Common form of fine grained, porcelanious masses and hardness
	Complex Tests	Effervesces in hot hydrochloric acid
	Popularity (1-4)	2
	Prevalence (1-3)	2
	Demand (1-3)	2
	Distinguishing Similar Minerals	The recently discovered, transparent Magnesite rhombohedrons appear identical to Calcite, but can be distinguished by the slight hardness difference, and more efficiently by the fact that Calcite effervesces even in cold and diluted hydrochloric acid, whereas Magnesite only in hot, undiluted hydrochloric acid. Dolomite - Cannot be distinguished from Magnesite by ordinary methods. However, Dolomite usually forms as curved crystals, whereas Magnesite does not.
	Commonly Occurs With	Calcite, Dolomite, Aragonite, Serpentine, Strontianite, Quartz, Brucite, Artinite
	Noteworthy Localities	Excellent specimens came from Oberndorf, Styria, Austria, and in St. Gotthard, Zillertal, Austria. Clear crystals identical in appearance to the Iceland Spar variety of Calcite occur in Brumado, Bahia, Brazil. Many localities exist on the west coast of the U.S., chiefly in the Coast Ranges of California. Also occurs in Bisbee, Cochise Co., Arizona; Gabbs, Nye Co., Nevada; South Canyon district, Dona Ana Co., New Mexico; and in Serpentine at Staten Island, (Richmond Co.), New York.
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