Andradite, like other garnets, forms rounded crystals with 12 rhombic or 24 trapezoidal faces or combinations of these and some other forms. This crystal habit is classic for the garnet minerals. Andradite is the calcium iron garnet and forms in contact or regional metamorphic enviroments as does grossular, the calcium aluminum garnet. It is believed that these garnets form from the metamorphism of impure siliceous limestones.
Andradite has many varieties based on color.
- Melanite is the black variety.
- Demantoid is the bright green variety and is sometimes cut as a gem.
- Topazolite is the yellow variety and is also occassionally cut as a gem.