1. (Science: geometry) related to the rhombohedron; presenting the form of a rhombohedron, or a form derivable from a rhombohedron; relating to a system of forms including the rhombohedron and scalenohedron.
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... To me. the "major names" would be the seven major crystal classes: triclinic, monoclinic, orthorhombic, trigonal, tetragonal, hexagonal/rhombohedral, or cubic. I gather the crystals you mention have something to do with plants. The first two at any rate are crystalline deposits of calcium ...
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