| Nissonite | |
| Category: | Phosphate mineral |
| Formula: | Cu2Mg2(PO4)2(OH)2·5H2O |
| Imasymbol: | Nss[1] |
| Strunz: | 8.DC.05 |
| System: | Monoclinic |
| Class: | Prismatic (2/m) (same H-M symbol) |
| Symmetry: | C2/c |
Nissonite is a very rare copper phosphate mineral with formula: Cu2Mg2(PO4)2(OH)2·5H2O. It crystallizes in the monoclinic crystal system typically as crusts, tabular crystals, and diamond-shaped crystals. The color is blue-green. It has a light green streak, a Mohs hardness of 2.5 and a specific gravity of 2.73. Cleavage is distinct.
Nissonite was discovered in 1966 and was named after William H. Nisson (1912–1965). It is from Llanada copper mine, near Llanada, San Benito Co., California.