plagihedral, a. Cryst.
(pleɪdʒɪˈhiːdrəl, -ˈhɛdrəl)
Also plagiedral.
[f. plagio- + Gr. ἕδρα seat, base.]
Having certain faces obliquely situated; also said of such faces.
| 1805–17 R. Jameson Char. Min. (ed. 3) 212 [A crystal is said to be] Plagihedral..when it has facets which are situated obliquely. a 1853 Pereira Pol. Light (1854) 257–8 In that form of quartz termed by Haüy plagiedral.., it has been found that when the unsymmetrical or plagiedral faces lean to the right, the polarization is right-handed, and, vice versâ. 1895 Story-Maskelyne Crystallogr. 316 A crystal of quartz..will, if right-handed, present on three alternate quoins at each end of the prism plagihedral faces arranged in the form of a right-handed screw. |