bipyramid

(redirected from Dipyramid)
Also found in: Encyclopedia.

bipyramid

(ˌbaɪˈpɪrəmɪd)
n
(Mathematics) a geometrical form consisting of two pyramids with a common polygonal base
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)
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 habit of the vein-type topaz as at Ouro Preto, Brazil, is characterized as being long and slender, terminated by a simple dipyramid {123}, and not at all like pegmatitic topaz.
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.
2]0}; one basal pinacoid, {0001}; and one dipyramid, {10[bar.
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.