The crystal structure of covellite has been refined, based on counter intensity data, to R=3.9%, using a crystal from Kosaka mine: P6₃⁄mmc, a=3.976(1), c=16.382(5)Å, Z=6. The structure proposed by Oftedal (Zeits. Krist., 83, 9–25, 1932) was confirmed. The S–S distance of the S₂ groups in the structure is 2. 086(7)Å, the Cu–S distance in the CuS₃ triangles 2.1915(4)Å, and the mean Cu–S distances in the CuS₄ tetrahedra 2. 313Å. The highly perfect cleavage characteristic of covellite may well be ascribed to the strong Cu–S bonds in the CuS₃ triangles which form, sharing corners, continuous sheets parallel to (001).

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The crystal structures of adamite, Zn₂(OH)(AsO₄), and its dimorph, paradamite have been refined. Adamite is the andalusite-type structure, and paradamite is isostructural with tarbuttite. The structures of these two minerals are compared. Mean bond lengths of these structures are:

	adamite		paradamite
As–O	1.69Å	1.68Å
Zn(VI)–O	2.13	–
Zn(V)–O	2.04		{	2.066
				2.06

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The structures of two polymorphs of MnSiO₃ have been determined from the single crystal X-ray data collected by a counter method. The rhodonite-type is triclinic, P-1, with a=7.616(3), b=11.851(5), c=6.707(2)Å, α=92°33′(6′), β=94°21′(6′) and γ=105°40′(6′), Z=10. The pyroxmangite-type is triclinic, P-1, with a=6.721(2), b=7.603(3), c=17.455(6)Å, α=113°10′(6′), β=82°16′(6′) and γ=94°08′(6′), Z=14. The structures of the rhodonite- and pyroxmangite-type were refined by full matrix least-squares method to the R-values of 0.050 and 0.071 for all 1664 and 1984 reflections, respectively. The configuration of the single silicate chains and coordination polyhedra in the MnSiO₃ polymorphs, indicates that the pyroxmangite structure consists of parts of the rhodonite and pyroxene structures.

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Coexistence of muscovites and paragonites with 2M₁ and 3T structures was found in one and the same hand rock specimen of zoisite-amphibolite from the Sanbagawa metamorphic belt, Shikoku, Japan. Both polymorphs of the muscovite and the paraganite have much the same chemical compositions, respectively. Their lattice constants and chemical compositions are given.

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