Category: Symmetrical habits
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Tetrahedral – Tetrahedron-shaped, triangular pyramid (four-sided)
Common examples include: tetrahedrite, spinel, sphalerite, magnetite
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Scalenohedral – Scalenohedron-shaped, pointy ends
Common examples include: calcite, rhodochrosite, titanite In crystallography, “regular” right “symmetric” “didigonal” (8-faced) and ditrigonal (12-faced) scalenohedra exist. The smallest geometric scalenohedra have eight faces, and are topologically identical to the regular octahedron. In this case (2n = 2×2), in crystallography, a “regular” right “symmetric” “didigonal” (8-faced) scalenohedron is called a tetragonal scalenohedron.
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Rhombohedral – Rhombohedron-shaped (six-faced rhombi)
Common examples include: calcite, rhodochrosite, siderite
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Pseudo-hexagonal – Hexagon-like appearance due to cyclic twinning
Common examples include: aragonite, chrysoberyl
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Prismatic – Elongate, prism-like: well-developed crystal faces parallel to the vertical axis
Common examples include: beryl, tourmaline, vanadinite, emerald
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Octahedral – Octahedron-shaped, square bipyramid (eight-sided)
Common examples include: diamond, fluorine, fluorite, magnetite, pyrite
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Hexagonal – Hexagonal prism (six-sided)
Common examples include: emerald, galena, quartz, hanksite, vanadinite
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Equant/Stout – Length, width, and breadth roughly equal
Common examples include: apophyllite, olivine, garnet
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Enantiomorphic – Mirror-image habit (i.e. crystal twinning) and optical characteristics; right- and left-handed crystals
Common examples include: gypsum, quartz, plagioclase, staurolite
