Summary: Biphosphammite, NH₄H₂PO₄, recorded once as secondary powder in 1870, occurs with bat guano in Murra-el-elevyn cave, 31° 20′ S., 126° 0′ E., Western Australia.

The mineral occurs as tapering tetragonal prisms with pyramidal terminations, which are colourless to light buff, very soft, water soluble, contain fine syngenite inclusions, and have D 2·04, ω 1·525, ε 1·480 Space group I4¯2d, a 7·4935 Å, c 7·340 Å, six strongest powder X-ray lines 3·75 Å (10) 200; 5·24 Å (9) 101; 3·02 Å (9) 112; 1·993 Å (8) 312,213; 2·65 Å (7) 220; 2·368 Å (7) 310,301. Partial analysis of purest available material gave: P₂O₅ 51·1, K₂O 14·2, (NH₄)₂O 12·3, SO₂ 5·59, Na₂O 0·16, water-insolubles 0·81 per cent, remainder mainly CaO and H₂O. Calculated mineral content is 88 % biphosphammite (62 % NH₄H₂PO₄, 38% isomorphous KH₂PO₄), 11·5% syngenite, insolubles 0·81 % calc. total 100·3 per cent.

Material proposed to be neotype is preserved at the Government Chemical Laboratories, Perth, Western Australia.