† di-octaˈhedral, a. Cryst. Obs.
[di-2 1 + octahedral.]
Bounded by twice eight planes; i.e. having the form of an octahedral prism with tetrahedral summits.
| 1805–17 R. Jameson Char. Min. (ed. 3) 204 Di-octahedral topaz. |
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Restrict † Obs. to sense 1 and add: 2. Min. Of a mineral or mineral structure: having two out of every three octahedrally co-ordinated sites in the crystal lattice occupied.
| 1946 R. E. Stevens in Bull. U.S. Geol. Survey No. 950. 103 The formulas of biotite..and of talc...are trioctahedral..whereas those of muscovite..and pyrophyllite..are dioctahedral, having one vacant octahedral position in the formula. 1953 [see illite n.]. 1967 Oceanogr. & Marine Biol. V. 155 They did..contain about 10{pcnt} of dioctahedral montmorillonite together with traces of anhydrite, calcite, and quartz. 1984 Greenwood & Earnshaw Chem. of Elements (1986) ix. 408 The gibbsite series is sometimes called dioctahedral..in obvious reference to the number of octahedral sites occupied in the ‘non-silicate’ layer. |