On the Occurrence of Crystallization in a Stucco-Casting

Abstract

In 1847–48, having been much engaged in plaster-casting at Bombay, in the spring of the latter year I had thrown out a multitude of useless fragments, when, on the 28th and 29th of March, a furious thunder-storm and fall of rain occurred at the setting in of the monsoon. A week or so afterwards, as soon as the weather slightly cleared up, what was my astonishment to find nearly all the fragments presenting crystals of semitransparent selenite on their surface! These, on examination, were found partly imbedded in the earthy mass of stucco, in part protruding above its surface. When the specimens were taken indoors, the crystallization extended itself, and the whole mass became covered over with fine pearly spicula, like the crystals of the finest actinolite, only not radiating from points. The stucco was prepared from a hard crystalline gypsum brought from the Persian Gulf; deprived of its water in the usual way, by being heated a little short of redness, then ground and sifted, and treated in the customary fashion. It was so absorbent that the rain disappeared from its surface almost as rapidly as it fell, so that the crystallization could not have arisen from saturation, in the ordinary sense of the term, or deposition from a menstruum.