Gypsa

When a ſmall quantity of any gypſum is melted together with borax, the glaſs becomes colourleſs and tranſparent; but I have found ſome ſorts of alabaſter and ſparry gypſa that, when melted in ſome quantity with borax, yield a fine yellow tranſparent colour, reſembling that of the beſt topaſes.

We find it tranſparent, of various Figures; but compoſed all of united Rhombs: and when its concretion has been interrupted, we ſee it in the forms of granulated, fibrous, or ſcaly maſſes, and call them Gypſa, or Plaiſter Stones.

The Iſle of Sheppey affords a kind of ſpar-like gypſa, of a fibrous nature, and always accreting like the radiations of a ſtar on the ſeptaria, and thence called ſtella ſeptarii.

The gypsum and rock-salt are found also in soils long posterior to the sand-stone with clay.—We have seen, that M. Steffens considers the gypsa of Lower Germany as making part of the chalky formation; and the salt-waters, which issue in that country, are referred to these gypsa and to the salt which they contain.

IV. Alabasters (Gypsa or Plaister stones)

17. Gypsa developed from anhydrites, grey gypsum-bearing limestones with bands of sandstones. The layer is covered with low-angle, turfy talus. Gypsa are white, grey, pink. Sandy limestones are light-grey. 22 m.

The gypsa are overlying conductive rocks which could correspond to a flysch formation with prevailing pelitic fraction. It seems therefore possible that the gypsa were squeezed out of the Tuscan nappe front and advanced towards NE together with the allochthonous covers.[…]They are the consequence of a very pronounced dissolution process in progress, affecting the deep gypsum layers. The river-bed dolines are visible every year in the September to November period, in relation with the minimum aquifer level in the gypsa after the summer drought.