| 单词 |
hemihedral |
| 释义 |
hemihedral, a. Cryst.|hɛmɪˈhiːdrəl, -ˈhɛdrəl|
Also hemiedral.
[f. hemi- c + Gr. ἕδρα seat, base + -al.]
Of a crystal: Having half the number of planes required by the highest degree of symmetry belonging to its system; thus, a tetrahedron is the hemihedral form corresponding to the holohedral octahedron.
1837[see hemihedron]. 1839–47Todd Cycl. Anat. III. 806/1 Triple phosphate..generally occurs in hemihedral six-sided prisms. 1850Daubeny Atom. Th. viii. (ed. 2) 264 All the crystals..were alike hemiedral..that is, half of their similar planes or angles were modified independently of the other half. 1878Gurney Crystallogr. 39 When the crystal has dissimilar faces at the two ends of the same axis of symmetry, the form to which those faces belong is called hemihedral.
Hence hemiˈhedrally adv.
1837Dana Min. ii. 19 Minerals, whose crystals are hemihedrally modified, are invariably thus modified, if the secondary planes occur, in which the hemihedrism may take place. |
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