bipyramid


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bipyramid

[¦bī¦pir·ə‚mid]
(crystallography)
A crystal having the form of two pyramids that meet at a plane of symmetry. Also known as dipyramid.
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References in periodicals archive ?
An important special case is the proper bipyramid [-1, 1] [direct sum] Q over Q.
1 We return once again to the bipyramid B, and its 1-dimensional spanning tree Y with edges 12, 13, 14, 15.
The crystals are tetragonal bipyramids and are, perhaps, the most easily recognized of the various crystallized species in the nodules.
The positions of trapezohedrons, bipyramids and twinning patterns in the form of damascence (visible laminations) on gwindels betray the presence of Dauphine twinning.
The new "Gouveia" thumbnails, by contrast, are isolated blue-black bipyramids to 2 cm, some having small red-brown rutile prisms lying flat on their faces.
The powellite crystals are loose, complete floaters, with white sprigs of scolecite protruding a millimeter or so here and there, and they are razor-sharp, textbook examples of tetragonal bipyramids, with c axes about 1.
1]11} bipyramids, modified by minor {001}, {010} and {100} pinacoids.
Pale blue-green crystals can be found on euhedral microcline where they form trigonal prisms and bipyramids.
I'll try to get this cleared up, but meanwhile I invite you to imagine the wondrous anatase crystals in a handful of specimens at Herb Obodda's stand at the Main Show: they are highly lustrous, lightly horizontally striated bipyramids with small basal faces on both ends.
The glittering white drusy quartz crusts do not disguise the sharp forms of the former tetragonal bipyramids of apophyllite; as before, the clusters reach cabinet size, with individual pseudocrystals to 4 cm.
Mirror-faced and brilliantly lustrous, smoky blue to maroonish gray scheelite bipyramids rest lightly on a pristine white matrix of drusy dolomite.
5 cm, with sparkling encrustations of colorless microcrystals of gmelinite; and what are probably the world's finest zircon specimens, with b rilliant red-brown simple tetragonal bipyramids to 9 cm in sugary albite with green aegirine needles, Finally, this locality, like Mont Saint-Hilaire, is a dreamland for micromounters, pseudomorph specialists, and rare-species aficionados generally.