trapezohedron


Also found in: Dictionary, Thesaurus, Wikipedia.

trapezohedron

[trə¦pē·zō¦hē·drən]
(crystallography)
An isometric crystal form of 24 faces, each face of which is an irregular four-sided figure. Also known as icositetrahedron; leucitohedron; tetragonal trisoctahedron.
References in periodicals archive ?
As a token of their evocative powers, whose effects are similar to the Trapezohedron's upon the unsuspecting Blake, the jewelry items in question manage to rouse strong emotions in the narrator of "Innsmouth" simply by means of "bald and prosaic" "fragmentary descriptions" ("Shadow," 310).
Finally, in a manner similar to Curwen's portrait, Pickman's canvases, the Shining Trapezohedron, the queer Innsmouth jewelry, the statuette of Cthulhu, and Zann's music, ekphrasis in "Picture" reveals that art serves as a vehicle for the exploration of the human psyche's inner depths.
The positions of trapezohedrons, bipyramids and twinning patterns in the form of damascence (visible laminations) on gwindels betray the presence of Dauphine twinning.
When trigonal trapezohedron faces (x) are present on a gwindel they typically benefit from the twist, as the x faces on the stacked component crystals are brought into planar alignment with each other and merge into one enlarged face.
The development of the different faces of this form is illustrated in Figure 3 which shows a stereographic representation of the faces of the trapezohedron. Crosses indicate faces projected onto the northern hemisphere, circles indicate faces projected onto the southern hemisphere, faces noted with heavy symbols occur on the garnet [i.e., (121), (211), (112), (112), (211), (121), (211), (112), (112), (121), (121) and (211)] and light symbols indicate faces of the trapezohedron that do not occur on the garnet [i.e., (211), (112), (121), (121), (112), (211), (112), (121), (211), (112), (211) and (121)].
The shapes of the belly bands (shaded) for the dodecahedron, the {211} trapezohedron, and the {321} hexoctahedron are given in Figure 19, along with the shapes of the (extended) belly band faces in their twins on [111].
The belly band of the {211} trapezohedron then corresponds to a hexagonal prism, but one that is rotated 60[degrees] with respect to the prism of the dodecahedron; i.e., it is the first order hexagonal prism {1010}.
Thus, we find that the isometric forms which can produce twins with belly bands composed of pairs of coplanar faces, one from each half of the twin, are limited to the dodecahedron, the {211} trapezohedron, and those hexoctahedra for which h = k + l.
Examples of first-rate Scottish zeolites in the two cases included very large specimens of basalt plates and open tubes lined with lustrous white stilbite "bowties" to 5 cm, thick coverages of lustrous white and colorless chabazite rhombs to 3 cm on matrix, perfect glassy analcime trapezohedrons to 2.5 cm sitting straight up on white calcite druses over basalt, red heulandite and blocky white hydroxylapophyllite crystals in stately groups, and, of course, the classic harmotome from Strontian, in magnificent crystal clusters with individuals to 3 cm across.
In their InnSuites room, Steve Behling and Sandor Fuss of Collector's Edge had laid out about 10 flats of matrix-plate specimens measuring from around 4 x 4 to 20 x 20 cm, with thick coverages of brilliant cinnamon-colored spessartine trapezohedrons, often with smoky quartz crystals to 4 cm, chalky white feldspar crystals to 1 cm, and tiny-but-sharp greenish hexagonal books of clinochlore, all these over a gray-white pegmatitic rock.
Further, Gilles had some new analcime specimens of a lovely, bluish white color, in lustrous trapezohedrons to 1 cm in groups up to 10 cm; in some miniatures, these "blue" analcimes come with clusters of bright yellow-brown curved siderite rhombohedrons averaging 5 mm.
Pollucite, a rare zeolite in a series with analcime, and crystallizing likewise in trapezohedrons, has popped up in soccer-ball-sized Pakistani crystals at shows before, strictly in a one-of-a-kind way.