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"...take any three edges formed by the intersection of three faces of a crystal. These axes are called the crystallographic axes, and the planes in which they lie are the axial planes. A fourth face on the crystal intersecting these three axes in the points A, B, C is taken as the parametral plan, and the lengths OA:OB:OC are the parameters of the crystal." -The Encyclopedia Britannica 1910

Crystallographic Axes of Reference

"...take any three edges formed by the intersection of three faces of a crystal. These axes are called…

"Crossed dispersion in a monoclinic crystal p>v." -Johannsen, 1908

Crossed Dispersion

"Crossed dispersion in a monoclinic crystal p>v." -Johannsen, 1908

"Horizontal dispersion in a monoclinic crystal. p<v." -Johannsen, 1908

Horizontal Dispersion

"Horizontal dispersion in a monoclinic crystal. p

"The symmetry of this class is as follows: The three crystallographic axes are axes of binary symmetry; the four diagonal axes are axes of trigonal symmetry; there are six diagonal planes of symmetry." &mdash; Ford, 1912

Symmetry of tetrahedral class

"The symmetry of this class is as follows: The three crystallographic axes are axes of binary symmetry;…