Crystal System.

Crystals formation is reflected by regular molecules arrangement inside of Minerals, which is called Crystal System. We can group all Minerals into 7 types.

1. Cubic, e.g. Diamond, Pyrite
2. Tetragonal, e.g. Cassiterite
3. Orthorhombic, e.g. Olivine
   
4. Monoclinic, e.g. Selenite
5. Triclinic, e.g. Amazonite
6. Hexagonal, e.g. Beryl
7. Trigonal, e.g. Calcite

~FJ, Natural Crystals & Gemstones.