orthopinacoidn.

1858 J. Nicol Elements Mineral. i. i. 33 Orthopinacoids and clinopinacoids are..distinguished from their position in relation to the axes.

1879 F. Rutley Study of Rocks x. 88 When the light falls obliquely either on the basal plane, the orthopinakoid, or the hemidome of a monoclinic felspar.

1912 W. E. Ford Dana's Man. Mineral. (ed. 13) 53 The orthopinacoid has two parallel faces, each of which intersects the a axis and is parallel to the b and c axis.

1925 Proc. Royal Soc. A. 108 241 The orthopinakoid a{100} is rare, and was only once seen on the seven crystals measured, but was then quite a prominent face.

1981 Jrnl. Pharmaceut. Sci. 70 1152 The bladed/lath-shaped crystals rest on one of the two large orthopinacoid (100) faces and present the microscopist with a single plane of optical symmetry.

1889 Q. Jrnl. Geol. Soc. 45 ii. 299 The Augite is almost colourless, and gives the usual eight-sided sections. Prismatic, ortho- and clinopinacoidal cleavages are present.

1920 Proc. Royal Soc. A. 98 77 The end faces of the prism are formed almost entirely by the faces of the primary prism p{110} and the orthopinakoidal form.