bipyramid

(redirected from Bipyramids)
Also found in: Encyclopedia.

bipyramid

(ˌbaɪˈpɪrəmɪd)
n
(Mathematics) a geometrical form consisting of two pyramids with a common polygonal base
References in periodicals archive ?
In a communication dated December 2004, Dr Johnson states "when I was investigating regular-faced solids in the early 1960s, there were no established names even for many of the obvious ones, except for pyramids and bipyramids.
More generally, we consider the possibly skew bipyramids
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.
I also purchased several sapphire crystals from this locality; they are medium to pale blue, very slightly stream-rounded, hexagonal bipyramids.
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.
Forms include a first-order and second-order prism, two first-order bipyramids, one second order bipyramid and the basal pinacoid.
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.