Speleothems of Great Onyx Cave, Kentucky, are composed of calcite, aragonite, and gypsum. Calcite is present in all carbonate samples, and where aragonite is also present, the speleothem core is always of calcite, overlain by a progression of alter- nating shells of aragonite and calcite, calcite being the outermost carbonate shell. In some specimens, gypsum encrusts these other two phases but is never itself enclosed by a carbonate, thus demonstrating that carbonate deposition was complete in these specimens before sulfate deposition began.
Cave temperature is constant at 12.5°C. The pH-values of standing and dripping water ranged from 7.5 to 8.7, with the value of 8.7 being recorded where precipitation and crystallization of calcite was taking place. At a pH of 8.7, some authors consider that calcium carbonate should normally crystallize as aragonite, but in the cave studied, pH seems to have little effect and temperature may be the controlling factor.
Strontium is measurable in most of the aragonite-bearing samples and not in the calcite ones. But two calcite stalactites and separated calcitic portions of mixed aragonite-calcite stalactites contain considerable quantities of strontium. Although the affinity of strontium for the aragonite lattice is demonstrated, it is probable that in these cave deposits, the strontium did not have a primary influence on the poly- morph which crystallized.