Crystallized Quartz; Cairn Gorum Crystals Enlarge
Dec.r 1. 1804. Publiſhed by Ja.s Sowerby. London.
British Mineralogy
CII
Silex Quartzum, crystallizum

Crystallized Quartz; Cairn Gorum Crystals

  • Class 2. Earths.
  • Order 1. Homogeneous.
  • Gen. 4. Silex.
  • Spec. 1. Quartzum.
  • Syn.
    • Quartz hyalin plagiédre. Haüy, v. 2. 413.
    • Quartz hyalin rhombifére. Haüy, v. 2. 413.

Cairn Gorum Crystals have been known for some years, and are said to have first caused the lapidaries to settle in Aberdeen, where they have been constantly employed in cutting them for seals, ring-stones, &c. They are perhaps of the oldest formation, and are found of various degrees of transparency, and sometimes are coloured yellow or brown. When a deep colour they are esteemed as topazes*, and if clear and large are sold at a high price. The brown ones are also valued if clear; but when of a bad yellow, or muddy brown, the lapidaries have recourse to their art, and prove them to be rock crystals, by dissipating their colour, and giving them a transparent lustre. See p. 88.

This specimen is remarkable for the face s of Haüy (i. e. the little narrow face in the middle of the right-hand outline, which is often more regularly rhomboidal), being a truncation of the solid angle of the base of the pyramid; and the oblique face on the column, which is just below it, on the same outline, corresponding with the faces on the upper figure, so as to make them more distinct. This latter is on the right hand side of the column in most crystals on this group, and has not been before noticed. The next outline of a whole crystal lying on its column (from Cairn Gorum) has this face on the column on the other side, and a face on the edge of the pyramid and column, m of Haüy; which is somewhat rare. The left-hand outline has a little hollow in one corner, enclosing some liquid. The next figure shows the water, as it is commonly called, slightly magnified; which is mostly known by a little bladder of air moving as the crystal is moved. There is something that floats in the liquid, and looks like soot, or oxide of carbon. Crystals containing water or some liquid are sold at a high price. I do not know that any substance has been observed floating in the liquid within any crystal before.

The above group is in the collection of G. Laing, Esq. of Edinburgh. The other are in my own cabinet.

  • * Topazes are found in the Brazils, &c.
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