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XXXIII. The Power theſe Stones have of reſiſting the Force of Fire; is not from the ſame Cauſe with that of
ticles, aſſumed into it at the Time of its original Formation, as in the other Gems; and is thence yellowiſh, reddiſh, or bluiſh, and ſometimes, but very rarely, greeniſh. As the Diamond thus is ſometimes of the Colour of other Gems, but greatly ſuperior in Hardneſs to them; ſo the common Cryſtal, ſometimes, from the ſame Accidents, reſembles them, and is much ſofter, and of little Value. Cryſtals thus tinged are what the Jewellers call Baſtard Emeralds, Sapphires, &c.
The Diamond is compofed of various Laminæ laid cloſe one on another; and Jewellers of Skill will ſometimes find the Joinings, and with the Edge of a fine Inſtrument ſplit a Diamond into two of equal apparent Surfaces.
If the plain Surfaces of the Plates of a Diamond be turned to the Focus of the ſtrongeſt Burning-glaſs, it receives no Hurt, even by that powerful Fire; but if the Edges and Joinings of the Laminæ are turned to it, the Stone ſeparates at them, is reduced into a number of Scales or thin Flakes; and loſt.
The Form of the Brazil Diamond differs from the Oriental, as well as do its Qualities. There are Shirly, or Baſaltine, reſemblances of all the Oriental Gems; and this is ſuch of the Diamond; and no other. De Laet was acquainted with it, and with its qualities. Agricola knew its Dodecahedral form. Wallerius accurately deſcribes its Faces by their cubic Shape. The Bravil Diamond has the ſame Electric, and the ſame Phoſphoric Properties, with the Oriental: After it has been held in the Sun, it has a ſilvery Brightneſs in the dark; and the ſame Quality, in ſome Degree, when rubbed: and it takes the Foil, as the Oriental Diamond. But they all want the perfect Hardneſs of the Oriental Diamond; and they have ſomewhat leſs ſpecific gravity; and they can be melted by the extream force of Fire, which the Oriental Diamond cannot.
We are not to expect all Diamonds in their perfect cryſtalized form; we ſee them rounded in the Manner of the pebble Cryſtals, and like all other cryſtalized Stones, they vary in the Number of the Angles, even in the ſame Species.
Like all the other cryſtalline Stones, this is alſo liable to be tinged to all Colours; but theſe Tinges it receives in ſo ſmall a Quantity, and in a Degree ſo delicate, that it is a Doubt
