Abstract
Celestine from the Asaka gypsum mine, Fukushima Prefecture, was found as aggregates of grains on one side of flattened and elongated aggregates composed of subparallel arrangement of fibrous gypsum collected in the dump. This association is considered to be a hydration product of strontian anhydrite (SrO up to 0.94 wt.%) also found in the dump. The hydration process involved the preferential conversion of the CaSO4 molecule in the anhydrite into gypsum, but the SrSO4 molecule remained intact and eventually crystallized as celestine. The formation of such celestine was favoured by the absence of any hydrated strontium sulphate and the nature of gypsum excluding the substitution of strontium for calcium therein under the condition where such a hydration process took place.
