DITRIGONAL See also:

• BIPYRAMIDAL

BIPYRAMIDAL  CLASS FIG . 76.—Crystal of a m a m 582 Hexagonal bipyramid of the second See also:

• ORDER
• ORDER (through Fr. ordre, for earlier ordene, from Lat. ordo, ordinis, rank, service, arrangement; the ultimate source is generally taken to be the root seen in Lat. oriri, rise, arise, begin; cf. " origin ")
• ORDER, HOLY

order, bounded by twelve faces (s in See also:

• FIGS

figs . 99 and 8o) ; indices {II2I} {See also:

• IO2

IO2} . . Dihexagonal See also:

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

prism, consisting of twelve faces parallel to the hexad See also:

• AXIS (Lat. for " axle ")

axis and inclined to the See also:

• VERTICAL (from Lat. vertex, highest point)

vertical planes of symmetry; indices {hiko} . Hexagonal prism of the first order limo), consisting of six faces parallel to the hexad axis and perpendicular to one set of three vertical planes of symmetry (m in figs . 71, 78-8o) . Hexagonal prism of the second order {10o}, consisting of six faces also parallel to the hexad axis, but perpendicular to the other set of three vertical planes of symmetry (a in fig . 78) . Basal pinacoid {000t}, consisting of a pair of parallel planes perpendicular to the hexad axis (c in figs . 71, 78-8o) . See also:

• BERYL

Beryl (See also:

• EMERALD

emerald), See also:

• CONNELLITE

connellite, See also:

• ZINC

zinc, See also:

• MAGNESIUM [symbol Mg, atomic weight 24.32 (0 = 16)]

magnesium and See also:

• BERYLLIUM

beryllium crystallize in this class .