FMF - Friends of Minerals Forum, discussion and message board

[Rodney B Jackson]

Fantastic symmetry. The math is a bit deep for me though.

[chrisjacob]

Your discussion about the Tetrahedron penetration twin was very helpful for a newbie like me. I felt some parts very difficult to understand still the graph you shared help me in a better way to understand what you meant.






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CHris-

[Pete Richards]

The symmetry of tetrahedrite is a reduced isometric symmetry. The form {111}, for example, is a tetrahedron, not an octahedron. Thus a rotation of 90° about one of the axes introduces new symmetry elements and does not simply replicate the structure. I believe this is called twinning by merohedry.

Sorry, I now realize that I have missed a long and complex discussion....