The similarity between obtaining a “fix” of location and course by using a zenith camera to photograph the position of the stars, and determining the orientation of a crystal such as diamond or corundum by using the back-reflection Laue method has led to the term, crystal navigation. The two techniques are strikingly similar except that the crystal navigator does not need a chronometer. Longitude, latitude, and course have analogues in crystallography; and an error in “setting the course” or in determining a position may make a jewel bearing fail or a diamond cutter wear badly or break. The several crystal projections—sterographic, gnomonic, back-reflection Laue, and forward-reflection Laue—are discussed. The back-reflection projection and the gnomonic projection together constitute an efficient and reasonably simple system for crystal navigation. The technique of crystal navigation in corundum and in diamond is illustrated by charts. The practical usefulness of the system is shown by reference to diamond-tool design.

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