Book 27, Question 5
How many different crystal shapes are there?
Scientists sort crystals into seven main groups, called crystal systems, based on the shape of their repeating box.
These are cubic, tetragonal, orthorhombic, hexagonal, trigonal, monoclinic, and triclinic. Table salt is cubic. Quartz crystals look six-sided, but they belong to the trigonal group, while beryl is hexagonal. There are thousands of kinds of minerals, but they all fit into these seven families.