bipyramid

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bipyramid

(ˌbaɪˈpɪrəmɪd)
n
(Mathematics) a geometrical form consisting of two pyramids with a common polygonal base
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References in periodicals archive ?
Gmelinite is generally pink and vitreous with well formed colourless hexagonal dipyramid, prism and pinacoid crystals (Fig.
bicupola puboiliac (W2) bigyrate betraying (W3) birotunda obdurating (W3) dipyramid pyramidoid (OED) disphenoid hypnoidised (W2 has the -ize infinitive form) elongated delegation (W3) gyrate tragedy (W3) pyramid myriapod (W3) rotunda untoward (W3) triangular granularity (W3) Footnote:Pictures of all the Johnson solids are onlineatmathworld.wolfram.com/JohnsonSolid.html.
The morphology consists of a hexagonal prism and basal pinacoid modified by complex terminations consisting of up to three or four hexagonal dipyramid forms.
Lustrous, orange to red-orange, simple tabular wulfenite crystals modified along the edges by a dipyramid perch on, or are partly embedded in, white to pale gray calcite, without vanadinite or other associated species (Bideaux, 1990).
The crystals, reaching about 2 mm long, show dipyramid faces but no prism faces.
The rare Type III crystals, simple combinations of prism and dipyramid, are small and unzoned; they range from colorless to pale yellow and brown.
Large (to well over 3 cm) discoidal crystals of translucent green carbonate-fluorapatite were found in a habit consisting of only the low-angle hexagonal dipyramid. The crystals occur scattered generously over large to very large (over 46 cm) blocky crystals of while feldspar.
Milarite is hexagonal, its crystals nearly always being simple hexagonal prisms displaying at most four forms: two prisms, {10[bar.1]0} and {11[bar.2]0}; one basal pinacoid, {0001}; and one dipyramid, {10[bar.1]2}.
Crystal forms observed are the prism and dipyramid.
Morphologically the crystals exhibit the first-order prism {1010} and basal pinacoid {0001) with traces of the second-order prism {1120} and second-order dipyramid {1121} modifying the dominant forms.
A different, less common habit of calcite-II occurs as lustrous elongate prismatic crystals modified by a well-defined pinacoid and usually also the rare hexagonal dipyramid {7.7.14.2} They are transparent and colorless to very pale yellow, with horizontal striations on their prism faces.
He covers designing origami polyhedra, platonic and related polyhedra, and dipyramids and dimpled dipyramids.