Sulphate of Lime, or Acuminated or Spiculated Gypsum
- Div. 1. Crystallized.
This Gypsum is sonic of it remarkable for the acuteness of the angles, being more so than any described by Haüy or any other author; the oblique or inclining side being as it were elongated in a sort of accumulated steps, as in the upper left hand figure, is a new form with regard to the acute angle, and a facet at fig. 1, making it a seven-sided column. The two middle figures are varieties without that facet, and show some marks of the rising accumulation.
The upper specimen has varieties elongated, which are in the hollows of a small mass of chiefly granular Fluate of Lime of various tints. The right hand figure below has transparent spiculæ, with varieties of similar forms on the snowy white Gypsum. This is from Matlock, and the above from some other part of Derbyshire. The small spiculæ are nearly of the same nature, sticking on metastatic Carbonate of Lime. It is curious to see how distinct one substance may be from another, although in contact with it. Gypsum is also found in some parts of Derbyshire. &c. in loose spiculæ, as the bottom figure. Tab. 405. is related to these figures, but is much less acute. The manner of accumulation and smallness prevented our measuring these.