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LXXII. Many other Properties there alſo are in theſe Subſtances which are eaſily obſerved. As that ſome of the Stones before named are of ſo firm a Texture, that they are not ſubject to Injuries, and are not to be cut by Inſtruments of Iron, but only by other Stones[1].
LXXIII. On the whole, there is a great Difference in the Texture of the larger Stones; as may be learnt from the different Manners in which they may be worked; ſome may be cut, others engraved on, and ſhaped, as before obſerved, by the Turner's Inſtruments, as the [2]Magnet Gem, a Stone of very ele-
- ↑ This is a Doctrine well known to our Lapidaries, and without the Knowledge of which the Diamond, the firſt and fineſt of all Gems, never could have been worked into Form at all; for nothing will cut it but itſelf. Other Gems and Stones are either work'd with Diamond-powder, or with that of Emery, one of the hardeſt Subſtances in Nature, except the Diamond; and afterwards with Tripoly, and other ſofter Powders.
- ↑ The Magnet Gem, or Μαγνῆτις λιθος of the antient Greeks, I have before obſerved, was a Stone of an entirely different Nature from the Loadſtone, which we now call the Magnet. The Stone here meant, was a very bright white
mixed in the ſame Glebe. I have, from the Mines of Goſſelear in Saxony, a moſt elegant Piece of the foliaceous Orpiment, which has two fine Veins of native Sandarach running acroſs it: It was brought to me under the Name of a Gold Ore; and I believe really does contain a ſmall Quantity of that Metal.
