Minerals of the Wooltana Cave, Flinders Rangers, South Australia

Analysis of guano specimens from wooltana cave, formerly occupied by ghost bats (Macroderma gigas), shows the principal mineral is whitlockite with seven other crystalline phases. These include dittmarite NH₄MgPO₄H₂O, biphosphammite (NH₄K)H₂P0₄, syngenite K₂Ca(SO₄)2H₂O, gorgeyite K₂Ca₅(SO₄)₆H₂O, brushite CaHPO₄2H₂O, gypsum CaSO₄2H₂O and whewellite CaC₂O₄ H₂O. The mineralogy of the guano samples was determined by powder X-ray diffraction and field emission SEM and the phase analysis was quantified by Reitveld methods. Dittmarite is a very rare mineral and only reported from a small number of localities. It cannot be formed directly in caves as it is normally crystallised from boiling water. we propose that it is formed by decomposition of struvite, NH₄MgPO₄6H₂O, in the presence of ammonia arising from the fresh bat guano. The minerals dittmarite, struvite and newberyite, MgHPO₄3H₂O, can transform between themselves in caves and in kidney stones (in vitro) according to the conditions. Two minerals, gorgeyite, and whewellite, have not previously been reported from guano deposits. Gypsum and brushite are present in some samples and show up to 18% P04 for S04 in gypsum substitution and up to 18% SO₄ for PO₄ in brushite. Some pure end-member crystals were also identified. The whitlockite is also substituted by sulfate by up to 30% and averaging 10%. The cave walls are dolomite and a speleothem present shows calcite, magnesium calcite, gypsum and leonite, K₂Mg(SO₄)₂ 4H₂O an unusual sulfate mineral. The extent and presence of the sulfates and of whewellite confirms that substantial ground water has entered the cave consistent with the known wetter past climate.