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n.1.(Crystallog.) A name given to the two planes in the monoclinic system which are parallel to the vertical and orthodiagonal axes.
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
The crystals are minute, singly terminated, acicular laths elongated parallel to the c axis and tabular parallel to the orthopinacoid (100).
The author considered that it could be veszelyite, yet the crystal habit was quite particular, with a large (typical) "orthopinacoid" {100} which had not been observed in the original veszelyite.