Online Encyclopedia

BIPYRAMIDAL

Online Encyclopedia
Originally appearing in Volume V07, Page 577 of the 1911 Encyclopedia Britannica.
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BIPYRAMIDAL CLASS (Parallel-faced hemihedral). The elements of symmetry are a tetrad axis with a plane perpendicular to it, and a centre of symmetry. The simple forms are the same here as in the holosymmetric class, except the prism {hko}, which has only four faces, and the bipyramid {hkll, which has eight faces and is distinguished as a " tetragonal pyramid of the third order." Combination of Tetragonal Prism and Basal Pinacoid. combination of a bipyramid of the first order with a ditetragonal bipyramid and the prism of the second order. Compare also figs. 87 and 88. Examplesof substances which crystallize in thisclass are cassiterite, rutile, anatase, zircon, thorite, vesuvianite, apophyllite, phosgenite, also boron, tin, mercuric iodide.
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BIPYRAMIDAL CLASS (Parallel-faced aemihedral)

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