Mineralogy of cave deposits on San Salvador Island, Bahamas

Speleothem samples from ten caves located in the northeastern and southwestern corners of San Salvador Island (Bahamas) were analyzed by means of X-ray diffraction, scanning electron microscopy, and the electron microprobe. In addition to the prominent calcite, aragonite, and gypsum, already known to occur in San Salvador caves, eleven other minerals were identified. The minerals are celestite, SrSO4; cesanite, Na3Ca2(SO4)3OH; ardealite, Ca2(HPO4)(SO4)·4H2O; brushite, CaHPO4·2H2O; hydroxylapatite, Ca5(PO4)3OH; fluorapatite, Ca5(PO4)3F; chlorapatite, Ca5(PO4)3Cl; collinsite, Ca2(Mg,Fe)(PO4)2·2H2O; witlockite, β-Ca3(PO4)2; niter, KNO3, and nitratine, NaNO3. Cesanite has not been previously reported from a cave. This is the second reported occurrence of collinsite.San Salvador Island, on the eastern edge of the Bahamian Platform, is the location of a large number of relatively small flank margin caves. In adition TO the more obvious speleothems — stalactites, stalagmites, and flowstone — the San Salvador caves contain a variety of crusts and soils of unknown mineralogy. This paper is an account of an investigation of samples collected from ten of these caves. Prior to the result reported here, only calcite, aragonite, and gypsum had been identified in the various speleothems from caves on San Salvador Island (Vogelet al. 1990; Schwabeet al. 1993).