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Bustamite is a calcium manganese inosilicate (chain silicate) and a member of the wollastonite group. Magnesium, zinc and iron are common impurities substituting for manganese. Bustamite is the high-temperature polymorph of CaMnSi2O6 and johannsenite is the low temperature polymorph. The inversion takes place at 830 °C, but may be very slow.〔Deer, W A, Howie, R A and Zussman, J (1978) Rock-Forming Minerals, 2nd edition, Volume 2A, pages 574-585〕 Bustamite could be confused with light-colored rhodonite or pyroxmangite, but both these minerals are biaxial (+) whereas bustamite is biaxial (-). ==Cell parameters== There is considerable variety in the literature about the size and type of the unit cell, the formula to be used, and the value of Z, the number of formula units per unit cell. Bustamite is a triclinic mineral, which could be described by a primitive unit cell, but the larger A-centered cell is often preferred, in order to facilitate comparison with the similar mineral wollastonite.〔Peacor and Prewitt (1963) The American Mineralogist volume 48 pages 588 to 596〕 The formula for bustamite is CaMn(SiO3)2〔 but it is sometimes written (Ca,Mn)SiO3, and changing the formula in this way will change the value of Z. The structure is chains of SiO4 tetraheda with repeat unit of three tetrahedra, unlike the pyroxenes where the repeat unit is two.〔 Ca++ and Mn++ are positioned between the chains. There are 12 tetrahedra in the A-centered unit cell.〔 The unit cell, the formula and Z cannot be taken separately; they are interlinked and form a consistent set of values. In this article we adopt the A-centred unit cell (space group A) with a = 7.736 Å, b = 7.157 Å and c = 13.824 Å, the formula CaMn(SO3)2 and Z = 6. Deer et al.〔 take the formula as (Mn,Ca,Fe)() so their value of Z is doubled to 12. Mindat〔 apparently gives the lattice parameters for a face-centred cell,〔 although they give the space group as P. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「bustamite」の詳細全文を読む スポンサード リンク
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