Tourmaline, or Schorl Enlarge
May 1. 1807. Publishd by Ja.s Sowerby. London.
British Mineralogy
CCX
Argilla electrica

Tourmaline, or Schorl

  • Class 2. Earths.
  • Order 1. Homogeneous.
  • Gen. 4. Argilla.
  • Spec. electrical.
  • Syn.
    • Tourmaline. Kirw. 1. 271.
    • Le Schorl. Broch. 1. 226.
    • Schwarzer Schorl. Emmerl. 1. 95.
    • Tourmaline. Haüy, 3. 31.
    • Borax electricus. Linn. Syst. Nat. ed. 12. t. 3. 96.

The present specimen is part of a large aggregated* mass sent me by the Rev, Mr. Gregor from Cornwall, and is composed of numerous crystals forming several distinct varieties, where they are not confusedly intermixed with each other. It seems to have been found in the vicinity of a red Oxide of Iron, as the colour about it indicates. In Mr, Gregor’s account of the analysis (Nicholson’s Journal, vol. 4. 312), it appears that it contains Oxide of Titanium. It is somewhat remarkable that the red Schorl of Siberia, and the large specimen of Rubellite or Titanite (as it has been called) in the possession of the Right Hon. Charles Greville, are by sonic considered as varieties of Tourmaline.

The crystals in this specimen show many of the faces which are generally found on Tourmaline ; viz. the three-sided prism, truncated at the edges, and formed into a six-sided prism, the same with two or more bevillings on the edges, &c.—The fracture is somewhat conchoidal, and the primitive form is a rhomboidal parallelopiped.

Tourmaline is harder than Quartz. With moderate heat it becomes electric, attracting and repelling ashes, &c., a property said to be in Schorl, Bergm. 2. 124. Kirw. 1. 272. The latter observes that Bergman thought Lime essential to Schorl in the analysis of that of Mount Albans, which Mr. Kirwan says was probably Hornblende.

Mr. Kirwan asserts that Schorl was named so from its brittleness; others say from the village Schorlow where it was first noticed.

Analyses of Tourmalines by Bergman.
Of Tyrol. Of Ceylon. Of Brazil.
Argill 42 39 50
Silex 40 37 34
Calcareous Earth 12 15 11
Iron 6 9 5
100 100 100
Analysis of the Tourmaline of Brazil by Vauquelin.
Silex 40.00
Alumine 39.00
Lime 3.84
Oxide of Iron 12.50
Oxide of Manganese 2.00
Water 2.66
100.00
  • * Schorl is said to be mostly aggregated, and Tourmaline to be chiefly imbedded in single crystals.
  • † This was presented to Colonel Symes by the king of Ava, and is said to be worth a thousand pounds.
  • ‡ Foreign specimens, sometimes cut and polished, are known by this property.
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