How many types of grain are there?

Grains are crystalline structures of different sizes. While no two grains are truly alike in terms of absolute size, their repeated crystalline structure can only be composed in 14 different ways: triclinic (1 type), monoclinic (2 types), orthorhombic (4 types), tetragonal (2 types), hexagonal (2 types), and cubic (3 types).