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barytocalcite
Barytocalcite is an anhydrous barium calcium carbonate mineral with the chemical formula BaCa(CO3)2. It is trimorphous with alstonite and paralstonite, that is to say the three minerals have the same formula but different structures.〔 Baryte and quartz pseudomorphs after barytocalcite have been observed.〔
Barytocalcite crystallizes in the monoclinic crystal system, typically as massive to druzy accumulations of transparent white to yellow to grey aggregates of slender prismatic crystals. It has a Mohs hardness of 4 and a specific gravity of 3.64 to 3.71.〔
It was first described in 1824 for an occurrence in the Blagill Mine in North Pennines, Cumbria (Cumberland), England, and named for its composition.
==Structure==
The mineral crystallises in the monoclinic crystal system. Most sources〔〔〔 put it in the prismatic class 2/m, with space group P21/m, but Webmin〔 puts it in the sphenoidal class 2 with space group P21. The structure is similar to that of dolomite, but with two crystallographically different CO3 groups.〔 The cation layers are stacked in an ABCABC... stacking pattern, repeating every 3 layers. The Ca ion is coordinated to 7 oxygens.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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