. The Bell System technical journal . t the prism faces neverare. On the prism face, true prism faces that are very short in the 2 direc-tion alternate with short rhombohedral faces to give the general contoura slant. These steps give the face a striped look. The stripes are knownas growth lines or striations. They are parallel to x and used tofind -v to a degree or so. If we sight on striations on two adjacent faceswe can locate the optic axis to nearly the same accuracy since the opticaxis is perpendicular to the striations on all faces. There are several indications that help us find
. The Bell System technical journal . t the prism faces neverare. On the prism face, true prism faces that are very short in the 2 direc-tion alternate with short rhombohedral faces to give the general contoura slant. These steps give the face a striped look. The stripes are knownas growth lines or striations. They are parallel to x and used tofind -v to a degree or so. If we sight on striations on two adjacent faceswe can locate the optic axis to nearly the same accuracy since the opticaxis is perpendicular to the striations on all faces. There are several indications that help us find, from the prism, wherethe major rhombohedron would be in the absence of such faces. Somecrystals grow in the form shown in Fig. They are symmetricallydoubly terminated and a very narrow prism is found under the majorrhombohedron, a wide face under the minor. Hence given a portion likethat enclosed in the dotted line we could deduce the complete orientation. Some crystals grew out at right angles to a wall and because they grew. REFERENCETABLE Fig. —Optical orientation by reflection of light from faces
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