hemitropicadj.
/hɛmɪˈtrɒpɪk/ Crystallography.
Said of a composite or twin crystal: see quots.
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hemitrope1816
hemitropic1886
1886 F. W. Rudler in Geol. Mag. III. 267 The edges of the hemitropic lamellæ are too blurred to allow the exact angles to be taken.
1895 N. Story-Maskelyne Crystallogr. §154 Two crystals are said to be hemitropic or twinned when, presenting identical forms, they are united together in such a way that, if we conceive one of them as being turned through half a revolution round a particular line which wil' be termed the twin-axis..corresponding faces and edges in the two crystals would become parallel.
1895 N. Story-Maskelyne Crystallogr. §159 In the case of two hemitropic diplohedral crystals, the twin plane becomes in a crystallographic sense a plane of symmetry to the twin-structure; but..each crystal in the hemitropic group retains its individuality, notwithstanding the mutual interpenetration of the crystals.
This entry has not yet been fully updated (first published 1898; most recently modified version published online June 2018).
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adj.1886