† sexoctonaladj. [after sexduodecimaladj., sexdecimaladj.] CrystallographyObsoleterare (of a crystal) having six prismatic faces parallel to the central axis and eight faces at each pyramidal end, or vice versa.
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1816 P. CleavelandElem. Treat. Mineral. & Geol. 30 Plomb carbonaté (carbonate of lead) sexoctonal.