bipyramid

(redirected from Bipyramids)
Also found in: Dictionary.

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.
Mentioned in ?
References in periodicals archive ?
Forming suitable direct sums and (skew) bipyramids gives more smooth Fano d-polytopes with 3d - 1 vertices via
An interesting feature of most of the yellow, bipyramidal cryolite crystals is the conspecific epitactic overgrowth of small, lustrous, colorless cryolite crystals on the corners (represented by the pinacoids {001}, {010} and {100}) and on the crystal edges of the bipyramids (in the [011] zone).
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.
These include well-crystallized rods with a hexagonal cross section (elongated {110} dodecahedra), pseudohexagonal bipyramids and pseudoscalenohedra (the faces of both correspond to peculiarly developed {210} tetrahexahedra).
Finally, the Ledfords had ten large single crystals of Georgia lazulite, dug in 1999: sandy, pale blue loose bipyramids with some adhering white mica/quartz dust.
Nearly 50% of the wulfenite specimens found at the mine have acicular crystals which are very elongated bipyramids (only a small percentage of the wulfenite formed the more normal short bipyramids).
In addition to the old-time habit described above, it occurs in the brecciated sulfide-rich vein at the base of the Great Limestone, as sharp, lustrous, pseudohexagonal bipyramids typically to about 2 mm, but exceptionally reaching 1 cm.
Blanc area: groups of amethystine-tinged bipyramids, or smoky gwindels, or dreamy little fadens.
The anatase crystals are lustrous, very sharp, horizontally striated, fat blue-black bipyramids with small basal pinacoid faces; they reach an astonishing 3 cm long, and it is not uncommon to see crystals in the 2-cm range.
The crystals are slightly hoppered bipyramids to 5 cm high, occurring as singles and in groups of two or three, bright yellow, partly transparent, and fairly pretty.
Some specimens show generous sprinklings of maybe 15 bipyramids over a single face.