Description
Light smoky scepter crystal with a trigonal growth habit.
Size: 51 x 23 x 16 mm. 18 grams.
From Mexico
The term "trigonal" stands for a threefold rotational symmetry (as opposed to a sixfold symmetry of hexagonal crystals). Although quartz is trigonal by itself, certain crystal shapes make this more obvious. The most common trigonal habit is one where crystals lack z rhombohedral faces. The rhombohedral z-faces generally tend to be smaller than r-faces, and sometimes they are completely absent. Amethyst from geodes in basalt often lacks z-faces. Needle quartz often shows a trigonal habit, too.
Other habits with an obvious trigonal symmetry are the Muzo habit and the cubic habit. Trigonal growth habit is rare in scepter crystals.