Sulphate of Strontian

Some time in the year 1794 Mr. Tobin, of Bristol, first showed me, and was so good as to give me specimens of Sulphate of Strontian, from Redland, near Bristol; and it had been then but recently discovered, I believe, by himself, and was very little known. This was about the time Mr. Kirwan published his Elements of Mineralogy. We were next indebted to Mr. Clayfield for specimens, who, in 1797, discovered it at Aust Passage, near Bristol. The present figure is partly from one of his specimens. He observes that he discovered detached veins in different parts of the cliff. The strata in which the veins are found are nearly horizontal, consisting of Limestone in different hardnesses, and argillaceous Sandstone intermixed with Clay and Gypsum, and some of the fissues were filled up with Sulphate of Strontian from 3 to 12 inches in thickness.

The primitive appears to be a rhomboidal prism of about 105°, and 75° according to Haüy. Ours are a little truncated at the solid angles, otherwise they represent the primitive, and are nearer so than any we have seen or heard of.

The fractures are parallel to the primitive faces, and those of the upper and lower faces are brightest, and often show a sort of opaline lustre. Sometimes we can discern the two diagonal fractures. Cross fracture somewhat splintery, harder than Carbonate of Lime, and softer than Sulphate of Barytes. The natural colour is a little milky and somewhat blueish, whence Werner called it Celestine. It is nearly transparent. Spec. Grav. according to Mr. Clayfield from 3.88 to 3.96; the fibrous about 3.91. Analysis by Mr. Clayfield:

Sulphate of Strontian was in many cabinets before this discovery of Mr. Tobin, a Sulphate of Lime, or Sulphate of Barytes,—among others in the Woodwardian Collection at Cambridge, as I am informed by Professor Hailstone.

It is found in Sicily, Mont-Martre near Paris, and in America. Those of Sicily are said to be the finest, and are columnar, not tabular like the Bristol ones.