A new calcium aluminum silico-phosphate mineral has been found at two locations on Newry Hill, Newry, Maine, U.S.A. Its composition closely approximates to 3CaO.3·5Al₂O₃.3SiO₂.2P₂O_5.18H₂O (Z = 1). Perhamite is uniaxial (+), c = 1577, ω = 1·564, density = 2·64 g/cm³. The mineral is hexagonal, probably P6/mmm, with a = 7·02 Å, c = 20·21 Å. The colour is light brown to white, the habit is as aggregates of discoidal hexagonal crystals. Cleavage is perfect {0001}, the lustre is vitreous, and the streak white. The mineral is named for a pegmatite miner and geologist, Frank C. Perham of West Paris, Maine, U.S.A.

The most similar species is viséite. A re-examination of viséite indicates that the composition previously given is incorrect. A new form of viséite, also from Visé, Liège, Belgium is also examined and found to differ in composition from the type material.