Subsulphate of Alumine
- Class 2. Earths.
- Ord. 1. Homogeneous.
- Gen. 1. Argilla.
- Spec. 3. Subsulphate.
- Subsulphate of Alumina. Thomson’s Annals, 2. 238.
- Alumine Pure. Haüy Tab. 58.
- Pure Clay. Jameson, 1. 294.
- Native Argill. Kirw. 1. 175.
Some time since my first acquaintance with the indefatigable Mr. Mautell, he sent me, along With Crystallized Carbonate of Lime in Chalk, (see Brit. Mini tab. 457.) and other things from Beaehy Head, a specimen, which I put on one side to examine when opportunity offered, as it presented to me a new appearance. I was soon after favoured by Mr. Brando with a specimen of pure Clay from the Cliff at New haven in Sussex, and was struck with their similarity: they have since proved to be actually the same; for Mr. Mantell found his specimen among some Beach stones near Lewes, which had been brought from Newhaven, where Mr. B. found it, and from whence Mr. M. has sent me additional specimens. By careful examination, Dr. Wollaston and Mr. Smithson have found it to be a Subsulphate of Alumine. See Thomson’s Annatels, v. ii. 238.
The description of pure Clay from Halle in Saxony (in Kirwan, and most authors since,) accords so well with this substance, that I feel no hesitation in pronouncing it to be the same; it apears also to occur in a similar situation, as it is accompanied by Gypsum.
It has been suspected by Widenmann and others, that the pure Clay of Halle is only the refuse of some chemical laboratory; Jameson, however, says that its external shape is sufficient to prove it a natural production. The Gypsum that accompanies it, and a similar substance being found in other places where no doubt can arise, confirm his opinion. I am much gratified that this question is settled by specimens discovered in my own country, making a valuable addition to British Mineralogy.—I here quote my assiduous friend’s letter on his sending it me from Newhaven, in which he describes its locality: “It occurs both stratified, and in tuberose masses, upon the Chalk, and under a stratum of Sandstone. The first reaches to a great height, perhaps two or three hundred feet above the shore; and as there are several distinct strata of Marle above the Subsulphate of Alumine, it is impossible to obtain any of the latter immediately from its native bed without exposure to considerable danger. Large fragments of the cliffs are, however, frequently falling down, so that a pretty good supply may generally be procured. I consider myself very fortunate in meeting with such beautiful specimens, as two French gentlemen had been collecting it but a short time since.”—When fresh gathered it is somewhat unctuous to the touch; it has a horny semitransparency, and is perfectly white; when dry it is smooth but not unctuous, and is opaque; it does not adhere to the tongue, but rubs off on the finger; when wet it cuts like soap, when dry it is smooth, and very soft under the knife; a low red heat renders it friable: according to Kirwan it is infusible at 166° of Wedgwood.
The analysis of a specimen from Halle gave Fourcroy,
|Sulphate of Lime||24|
|Lime, Silica, and a Muriate||4|
while Mr. Simon of Berlin found
The Rev. Mr. Western has given me specimens exactly like ours, but smaller, from Lissey in Moravia.
The upper specimen has a very little ochraceous Marle about it in the crevices, and the tuberose appearance is rather smaller than usual: but smaller and larger masses resembling the head of a cauliflower, &c., are found, which differ but little from it. The lower figure is somewhat more crumbly, and surrounds a fragment of Common Flint Pebble. Masses of Marie and Crystallized Sulphate of Lime, more or less coloured by Iron Ochre, often accompany these nodules. The Subsulphate of Alumine appears to result from the decomposition of Iron Pyrites, producing Sulphate of Iron, which is again decomposed by the Clay or Lime.