Earthy Talc. Green Earth of Veraw. Terre verte Enlarge
June 1. 1808. Publish’d by Ja.s Sowerby London.
British Mineralogy
CCLXXII
Silex talcum

Earthy Talc. Green Earth of Veraw. Terre verte

  • Class 2. Earths.
  • Order 1. Homogeneous.
  • Gen. Silex.
  • Spec. Talcum.
  • Div. 3. Amorphous.
  • Syn. Green Earth. Kirw. 1. 196.

Said to be found near Verona, as well as in Bohemia, &c. also in Scotland, and Somersetshire. The present specimen came from the Hill of Kinnoul in Scotland. It is the largest piece I have ever seen, and was lent me by G. B. Greenough, Esq. It is to be found entrapped in a smoothish earthy rock in various forms and of different sizes. I know not if it could be gathered so pure as to serve for commerce there or any where else in Great Britain; but if it could, I should think it might be chosen of such tints as might be desirable to artists, it being very durable. It may probably be the pigment used in the large draperies often exhibited in pictures of the Venetian school, so much admired by connoisseurs for their brilliant and lasting greens. Mr. Kirwan thought the green colour was owing to a mixture of “Calx of Nickel.” It is not, however, known at present what gives permanent colour to most mineral substances, iron in this scums to he particularly oxidated, so as to serve that purpose, perhaps with the help of a peculiar phosphate of a blue colour, mixed with a certain yellow Oxide, or Sulphur, these being so nicely incorporated in the mass as not to be easily detected. Most endeavours to ascertain the colours of substances first discolour them, and it is not easy to find and mix the proportions by synthesis, although the present advancing state of chemical knowledge gives a hope that these things are likely to be discovered in due time.

The analysis by Klaproth shows no particular colouring substance except Iron, as will be seen below:

Silica 53
Alumina 12
Magnesia 3.5
Lime 2.5
Oxide of Iron 17
Water 11
Loss 1
100.0

The holes in the Rock of Kinnoul are occasionally lined or tilled with great variety of coloured substances, perhaps including all possible mixtures, except the more brilliant reds and crimsons.

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