Montgomeryite is a phosphate mineral with the chemical formula Ca<sub>4</sub>MgAl<sub>4</sub>(PO<sub>4</sub>)<sub>6</sub>(OH)<sub>4</sub>÷12H<sub>2</sub>O. The mineral was discovered in Fairfield, Utah in a variscite nodule. Montgomeryite is a very rare mineral and can only be found in a few places in the world.