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by means of the Humidity of the metalline Matter of which they partake; or of their own Nature: and in this Manner the Pyritæ alſo, and thoſe Kinds of them called the Molares, melt with the Matter they. are laid upon in burning.
lour from, and in ſome Degree impregnated with the Virtues of the metalline Matter, among which it is deſerted by the Water wherein it was before ſuſpended; and left to coagulate, and aſſume the Form naturally ariſing from the Concretion of its Parts. Where theſe Spars are formed out of the Reach of metalline Matter, and have received, in their Paage through the Strata, no Impregnations from it, they are white: this is the natural Colour of their conſtituent Particles. But where they are formed in or about Mines, they, as our Author very juſtly remarks, partake of the Nature of, and, in ſome Degree, owe their Form and Mode of Exiſtence to the particular Metal of the Mine. Their Shape and Virtues are often given them by the metalline Particles mixed with them in their Concretions; their Colours always; and that in a ſtronger or fainter Degree, as there has been more or leſs of that Matter mingled in their Maſſes[B 1].
If the metalline Particles are in the Mixture in any conſiderable Quantity; the whole aſſumes a Shape peculiar to the Metal to which they belong; if that be Lead, the ſparry Concretions are cubic; if Iron, rhomboidal; and if Tin, they, ſhoot into the Form of quadralateral Pyramids. Theſe are the Metals of which we can pretty certainly judge, from the Figure of the Spar about the Mine: as for the others, though they, influence the ſhooting of it in no leſs Degree, yet they do not always throw it into ſuch determinate or regular Figures.
But if the metalline, Particles, aſſumed into the Spar at the Time of its Concretion, have a very great Power in determining it to a certain Figure; the Influence they have over it, in regard to Colour, is much greater; as all that it has of that is wholly owing to them: and as they are in greater or leſſer Quantities: in it, they give it different Degrees, from the ſlighteſt Tinge to the deepeſt Colour.
What Metal has been concerned in effecting
- ↑ See Appendix.
