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PLAGIHEDRALI CLASS

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Originally appearing in Volume V07, Page 576 of the 1911 Encyclopedia Britannica.

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PLAGIHEDRALI CLASS (Plagihedral-hemihedral; Pentagonal icositetrahedral; Gyroidal 2). In this class there are the full number of axes of symmetry (three tetrad, four triad and six dyad), but no planes of symmetry and no centre of symmetry. Pentagonal icositetrahedron (fig. 40). This is the only See also:

SIMPLE

simple See also:

FORM (Lat. forma)

form in this class which differs geometrically from those of the See also:

HOLOSYMMETRIC

holosymmetric class. By suppressing either one or other set of alternate faces of the hexakis-See also:

OCTAHEDRON (Gr. 6K-rw, eight, Mpa, base)

octahedron two pentagonal icositetrahedra {hkl) and (khl) are derived. These are each bounded by twenty-four irregular Icositetrahedron. See also:

DODECAHEDRON (Gr. Melia, twelve, and ESpa, a face or base)

Dodecahedron. pentagons, and although similar to each other they are respectively right- and See also:

LEFT

left-handed, one being the See also:

MIRROR (through O. Fr. mirour, mod. miroir, from a sup-posed Late Lat. miratorium, from mirari, to admire)

mirror See also:

IMAGE (Lat. imago, perhaps from the same root as imitari, copy, imitate)

image of the other; such similar but nonsuperposable forms are said to be enantiomorphous (evavrios, opposite, and µop¢$, form), and crystals showing such forms sometimes rotate the See also:

PLANE

plane of polarization of plane-polarized See also:

LIGHT

light. Faces of a pentagonal icositetrahedron with high indices have been very rarely observed on crystals of See also:

CUPRITE

cuprite, See also:

POTASSIUM [symbol K (from kalium), atomic weight 39.114 0=16)]

potassium chloride and ammonium chloride, but none of these are circular polarizing.

End of Article: PLAGIHEDRALI CLASS

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