dipyramid


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dipyramid

[dī′pir·ə‚mid]
(crystallography)
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The habit consists of the tetragonal dipyramid capped by the basal pinacoid, and ranges from rather flattened (dominant c face) to steep dipyramids, all with excellent luster and sharpness.
Faces of the trigonal dipyramid s{1121} are often present, but faces of trigonal trapezohedra such as x{5161} have not been observed.
He covers designing origami polyhedra, platonic and related polyhedra, and dipyramids and dimpled dipyramids.
The mineral, at first thought to be a form of barytocalcite, is trimorphous with bary-tocalcite and paralstonite, and forms white to colorless or faintly pink acute pseudohexagonal pyramids or dipyramids up to 6 mm long.
The mineral is trimorphous with barytocalcite and paralstonite, and forms white to colorless or faintly pink acute pseudohexagonal pyramids or dipyramids up to 6 mm long.
The other 40% of the zircon grains are stubby to slightly elongate, euhedral, clear, colourless multifaceted dipyramids with an average length to breadth ratio of 2.
By new-new I mean that the wulfenite crystals are simple, flat-topped tetragonal prisms with a length-to-width ratio of around 2:1, although there is also a minority of the spiky dipyramids.
Prismatic crystals show major {001} and minor {010} pinacoids, prominent {011} and {012} prisms, terminated by {21l} dipyramids (usually etched).
Thin-tabular, platy hematite crystals are common at many localities; these crystals generally have large, wide {0001} faces rimmed by positive and negative rhombohedrons {1010} and {0111}, in some cases also by first-order and second-order prisms {1010} and {1120} and/or dipyramids {1123}--the little "rims" outboard from the basal expanses, when wide enough to show faces at all, are commonly quite complex.
The crystal habit shows a combination of rhombic prisms and dipyramids.
The chief habits are highly elongated rhombic dipyramids or a combination of rhombic prisms and dipyramids.
These are solid pseudohexagonal dipyramids up to 1 cm each or more, sometimes in connected groups and clusters.