Some minerals, like gypsum, hold water in their crystalline structure. The activation energy of the dehydration reaction of gypsum is relatively low and the conversion of gypsum to bassanite (CaSO4H2O) or anhydrite (CaSO4) may take place at ambient conditions. Although still unexplored, the use of such crystallization water by organisms would point to a completely new water source for life, critical under dry conditions.

In this study we analyzed the hydrogen (2H) and oxygen (18O) isotope composition of the xylem water of shallow-rooted plants growing on gypsum, and compared it to the isotopic composition of the free and crystallization water of the gypsum soils where they grow. According to our results, the isotopic composition of the xylem sap of plants was closer to gypsum crystallization water than to free soil water, particularly during the dry summer. Bayesian stable isotope mixing models indicated that gypsum crystallization water accounted for up to 90% of the water used bythese species during summer. Plants could also uptake gypsum crystallization water during spring, when itaccounted for up to 30% of the xylem sap of plants. Although the underlying mechanisms require further research, this is the first experimental evidence in support of the role of gypsum crystallization water as a water source for life. Our results change the current paradigm on water use by plants, where water held in the crystalline structure of mineral rocks is not regarded as a potential source. Given the existence of gypsum on the surface of Mars and its widespread occurrence on arid regions worldwide, these findings have important implications for exobiology, the study of life under extreme conditions and arid land reclamation.

http://blogs.egu.eu/geolog/2015/04/22/drinkable-rocks/

Palacio, S., Azorn, J., Montserrat-Mart, G. and Ferrio, J. P.: Drinkable rocks: plants can use crystallization water from gypsum. Geophysical Research Abstracts Vol. 17, EGU2015-9011-1, 2015

Palacio, S., Azorn, J., Montserrat-Mart, G. and Ferrio, J. P.: The crystallization water of gypsum rocks is a relevant water source for plants. Nature Communications,5, 2014