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Tinsleyite in the ''dry'' Cioclovina Cave (Sureanu Mountains, Romania): the second occurrence

2002; Elsevier BV; Volume: 14; Issue: 1 Linguagem: Inglês

10.1127/0935-1221/2002/0014-0157

1617-4011

Ştefan Marincea, Delia-Georgeta Dumitraș, R. Gibert,

Subterranean biodiversity and taxonomy

This paper documents the occurrence of tinsleyite in the dry Cioclovina Cave, Sureanu Mountains, Romania. This is the first mention of tinsleyite as a cave mineral and the second find of this mineral species in the world. The mineral occurs in small quantities, as a rare authigenic, early diagenetic mineral, in the bat guano deposits in this cave. Low (alpha) quartz is the only closely associated mineral. This assemblage corresponds to a possible reaction in the natural guano - clay system upon decomposition of illite. Chemical analyses show variable leucophosphite contents (up to 31.68 mol.%). The unit-cell parameters calculated for an iron-poor sample are a = 9.638(5) A , b = 9.522(4) A , c = 9.540(4) A and b = 103.10(3)° , whereas those deter- mined for an iron-rich sample are a = 9.639(6) A , b = 9.538(8) A , c = 9.553(7) A and b = 103.04(4)° . Thermal analyses show that water is lost in three steps and that the loss of molecular water is complete before 250° C. The fully dehydrated material is com- pletely X-ray amorphous. Ammonium is expelled at about 490° C. The infrared spectrum of tinsleyite affords reasonable evidence for the presence of PO 4, NH4 and OH groups, together with H 2O molecules. The punctual symmetry of the PO 4 groups is C s.