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SCALENOHEDRAL CLASS (Bisphenoidal-hem...

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Originally appearing in Volume V07, Page 577 of the 1911 Encyclopedia Britannica.

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SCALENOHEDRAL CLASS (See also:

BISPHENOIDAL

Bisphenoidal-hemihedral) . Here there are only three dyad axes and two planes of symmetry, the former coinciding with the crystallographic axes and the latter bisecting the angles between the See also:

HORIZONTAL

horizontal pair. The dyad See also:

AXIS (Lat. for " axle ")

axis of symmetry, which in this class coincides with the See also:

PRINCIPAL

principal axis of the crystal, has certain of the characters of a tetrad axis, and is sometimes called a tetrad axis of " alternating symmetry "; a See also:

FACE (from Lat. fades, derived either from facere, to make, or from a root fa-, meaning " appear "; cf. Gr. cbatvstv)

face on the upper See also:

HALF

half of the crystal if rotated through 90° about this axis and reflected across the See also:

EQUATORIAL

equatorial See also:

PLANE

plane falls into the position of a face on the See also:

LOWER

lower half of the crystal. This See also:

KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind of symmetry, with simultaneous rotation about an axis and reflection across a plane, is also called " composite symmetry." In this"class all except two of the See also:

SIMPLE

simple forms are geometrically the same as in the See also:

HOLOSYMMETRIC

holosymmetric class. Bisphenoid (orpirv, a See also:

WEDGE (O. Eng. wecg, a mass of metal, cognate with Dutch wig, wigge, Dan. vaegge, &c.; in Lith. the cognate form outside Teut. is found in wagis, a peg, spigot; there is no connexion with " weigh," " weight," which must be referred to the root wegh, to li

wedge) (fig. 50). This is a See also:

double wedge-shaped solid bounded by four equal isosceles triangles; it has the indices lilt), 12111, 11121, &c., or in See also:

general 1hhll. By suppressing either one or other set of alternate faces of the tetragonal bipyramid of the first See also:

order (fig. 42) two bisphenoids are derived, in the Fig. 53 shows a See also:

COMBINATION (Lat. combinare, to combine)

combination of a tetragonal See also:

PRISM (Gr. rrpivµa, properly a thing sawn, Irpii"ety, to saw)

prism of the first order with a tetragonal bipyramid of the third order and the basal pinacoid, and represents a crystal of fergusonite. See also:

SCHEELITE

Scheelite (q.v.), See also:

SCAPOLITE (Gr. O'Kairos, rod, )tLOoc, stone)

scapolite (q.v.), and See also:

ERYTHRITE

erythrite (C4Hio04) also crystallize in this class.

End of Article: SCALENOHEDRAL CLASS (Bisphenoidal-hemihedral)

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