Formula: NaCaAl6(PO4)4(OH)9.3H2O hydrated phosphate containing hydroxyl, wardite group
Specific gravity: 2.83
Hardness: 5½
Streak: White
Colour: White to light grey, colourless in transmitted light.

Hydrothermal environments

Millisite is found in altered phosphate deposits. At the type locality, the Little Green Monster Mine, Utah, USA, it is associated with dehrnite, lewistonite and wardite.