Floating Rafts of Calcite Crystals in Cave Pools, Central Texas, U.S.A.: Crystal Habit vs. Saturation State

摘要

Calcite precipitation at the air-water interface in cave pools in central Texas (U.S.A) produces floating rafts of interconnected, low-Mg calcite crystals with individual crystal habits that range from equant (length to width = 1:1) to prismatic (4:1). Saturation state for the waters ranges from -0.19 to +1.35 (SI_c = log IAP/K). Equant crystals precipitate from waters with a lower saturation index (SI_c) and form rafts with a fused fabric whereas prismatic crystals precipitate from higher-SI_c waters and form rafts with an interlaced fabric. The pools contain low-magnesium (molal Mg/Ca < 0.6), calcium-bicarbonate, and calcium-bicarbonate-nitrate type waters with temperatures that range from 13.8°C to 20.7°C and pH readings from 6.7 to 8.4.