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XVIII. Some few of theſe Stones there are, which are ſubject to the Force of Fire, and may be burnt. Theſe ſhall be firſt treated of, in Conſideration of what their Differences are.
XIX. In regard to the Action of Fire on them, ſome are fuſible, and melt by it; as the metalline Kinds. For the Stones, which partake of the Nature of Metals, as Silver, Copper, or Iron,[1] melt in the Furnaces with them; either
- ↑ The Author is here treating of the various Kinds of Spars; formed near the Veins of different Metals, and aſſuming their Colours from, and partaking of the Natures of the particular Metals in the Mines of which they are found. All theſe are formed by the Percolation and Afflux of their conſtituent Matter, which is taken up by the Water continually pervading the Strata; and in its Way ſeparated from the groſſer Particles among which it was at firſt repoſited; and finally tinged with a Co-
which they had no particular Name, was the ſerving for Seals; they ſometimes, inſtead of diſtinguiſhing them by particular or deſcriptive Epithets, called them Seal Stones, and hence the Word Seal Stone, σφραγὶς or σφραγιδίον became with them a common Word for what we call Gem; and in that Senſe it is evidently uſed here by this Author.
Moſt of the Stones of this Claſs were found to be of ſo compact a Texture, as to reſiſt the Force of Fire; at leaſt of common Fires; and even of the ſtrongeſt known in this Author's Time; the ſolar indeed, which we are able to throw on Bodies, by reflecting Burning-glaſſes, no Stone, not even the Diamond, in all Circumſtances and Poſitions, can withſtand: But as ſome Stones, which he had yet to treat of, were ſubject to great Changes, from the Action of Fire, ſuch as was then commonly uſed on certain occaſions, whether culinary, or for the melting of Metals; theſe he firſt chuſes to deſcribe, and proceeds to give their ſeveral Differences.
