_Muscovy talck_ is remarkable for the thin and transparent flakes into which it is divisible, and thereby capable of various uses.
There are some other distinct species of earth, particularly one brought from Botany Bay, and another called _Stontiate_, from the place where it was found in Scotland; but they have not as yet been much examined.
All stones formed by nature are compounded, and to distinguish them from one another, and ascertain the parts of which they consist, is the subject of _lithology_, a very extensive branch of knowledge.
All the simple earths are nearly, if not absolutely, _infusible_; but when they are mixed they may all be fused.
Metallizable earths, commonly called _ores_, when united to phlogiston, make the metals, distinguishable for their specific gravity, their opacity, shining appearance, and fusibility.
All the proper metals are _malleable_, and those which are not so are called _semi-metals_.
The metals again are subdivided into the _perfect_ and _imperfect_. The former, which are _gold_, _silver_, and _platina_, suffer no change by fusion, or the longest continued heat: whereas heat calcines or dissipates the phlogiston of the imperfect metals, which are _mercury_, _lead_, _copper_, _iron_, and _tin_, so that they return to the state of earth; and this earth is always heavier than the metal, though of less specific gravity, having received an addition of weight from water or air: but these earths, or ores, being exposed to heat in contact with substances containing phlogiston, again become metals, and are then said to be _revived_.
The semi-metals are _bismuth_, _zinc_, _nickel_, regulus of _arsenic_, of _cobalt_, of _antimony_, of _manganese_, of _wolfram_, and of _molybdena_.
All metallic substances are crystallizable, and each in a peculiar form, which is discovered by leaving a hole in the bottom of the crucible in which they are melted, and drawing out the stopper, when the mass is beginning to lose its fluidity.
Some of the metals will not unite to others when hot, and others of them will; and such as will unite with others are called _solders_. Thus tin is a solder for lead, and brass, gold, or silver, for iron.
Ores are never found in regular strata, like the different kinds of earth; but in places which have formerly been cavities, running in all directions, with respect to the regular strata, and commonly called _veins_.