The 3T, 4T and 5T polytypes of wollastonite from Kushiro, Hiroshima Prefecture, Japan

Okayama Univ., Dep. Earth Sci., Okayama, Japan

Lattice constants: a = 23.2(1), b = 7.30(3), c = 7.06(3)Aa, alpha = 90.0 degrees , beta = 95.5(2) degrees , gamma = 94.6(2) degrees , a = 31.2(1), b = 7.30(3), c = 7.06(3)Aa, alpha = 90.0 degrees , beta = 95.5(2) degrees , gamma = 96.8(2) degrees , and a = 38.6(1), b = 7.30(3), c = 7.06(3)Aa, alpha = 90.0 degrees , beta = 95.5(2) degrees , gamma = 98.0(2) degrees . The stacking sequences were determined by the diffraction intensities of hk0 reflections as TTG, TTTG and TTTTG. The 5T ₁ polytype found is one of the three possible 5T polytypes. These polytypes occur in zoned skarns. The 3T, 4T and 5T ₁ polytypes were found in the idocrase zones, where both 1T and 2M coexist. Thus, the long-period wollastonite polytypes might form under the conditions intermediate between those under which the 1T and 2M polytypes formed.--Modified journal abstract.

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