the two first celebrated and accurate

mineralo

gists, when the object has been examined by them..

Explanation of a few abbreviations.

Every thing has been avoided, as much as pofsible, the meaning of which is not evident at first sight; however, a few remarks may not be improper on the columns, perfectly intelligible to those conversant with mineralogy. That of comparative hardnefs is taken from Mr Quist's table, the Swedish naturalist, as far as his extends; and the hardness of the rest are determined in his manner, by scratching one stone with another, or with steel. But his arrangement could not be followed in a table where scientific clafsification was observed, although it answered completely his view, which was merely to give an idea of that quality in gems, without attention to the form of their crystallization, chemical analysis, &c.

The hardnefs of the stones are exprefsed by numbers placed opposite their names, descending from No. 20 (that of the white diamond,) which is made the point of comparison; much in the same manner that the learned and ingenious vice president of the Royal Society, the honourable Daines Barrington, exprefsed the comparative notes of singing birds some years ago. It may be worth remembering, for those who wish to purchase precious stones, that all those not harder than No. 11, in our table, may be scratched with steel.

Mr Quist placed the stones, in his table, in such a manner, that every one was hard enough to scratch all below it in the co

lumn.

The column of acids may likewise require a few words of explanation to some, as the generic term; acid, is only wrote at the top of it, and the species 'indicated by a letter of the alphabet placed over the quantity found in a stone.

A. stands for aerial acid, or fixed air, F. fluor acid, P. phosphoric, T. tungsten, v. vitriolic.

In the column, iron, likewise, the letter D, placed over a quantity, indicates that the metal is dephlogisticated, or in the state of a calx.

The only remaining observation, necessary to render the table perfectly intelligible, is, that the terms oriental and occidental, as generally applied to gems, is not confined strictly to country. All the finest hard stones, of an uncommon water and colour, are commonly called oriental, wherever they may have been found; as the East Indies, in both ancient and modern times, has acquired the first reputation for such productions; although both America, and some parts of Europe, furnish the jewellers with gems of great beauty and value, which are often sold undèr the denomination oriental, as a sure claim to prefeOur Siberian aque marine, for example, I make no doubt is sold in other countries as such, to the great profit of the vender; at the same time that the purchaser will be no loser by the imposi

rence.

tion.

A few words are likewise necefsary to justify some additions, which the author of the table has taken the liberty of making, to render it more generally useful, not alone to men of science, but to the public at large.

1st, He has added to each order, (but in such a detached manner as not to interfere with scientific arrangement,) a few articles sold and worn as gems, although belonging to other classes of mineralogy, vix. the turquoise and pearl added to the first order, the one mineralized ivory, the other a species of animal production, formed by a number of coats or layers, like other animal calculi.

The malachite, so much resembling a beautiful green stone, and as such so much employed in ornamental trinkets, he has likewise taken the liberty of adding to the second order, in the same good intention, although of metallic origin; a circumstance very indifferent to the public at large. However, as said above, those heterogeneous bodies are noted in a detached section, in such a manner as not to hurt the feelings of scientific nomenclators. But for the rest of his additions he will make no apology, even to them, as they can be defended on principles of mineralogy; or rather no well founded scientific reasons can be urged against the rank afsigned them as precious stones, being generally either late discoveries, not sufficiently known when the different systems were formed, or such stones, as from their beauty, value, and public estimation, merit a place in one or other of the orders of precious stones, when no good reason can be given for depriving them of it. However, to enable every one to judge for himself, all such additions are acknowledged in the article that treats of them, and the reasons given which induced the author to place them there. The additions to the first order are:

The garnet and tourmaline, not generally classed in it by authors, although not entirely innovations of his own; as will be seen in the table.

The opal and cat's eye, two valuable and beau- . tiful gems, in high estimation, universally excluded, for reasons which fhould not even influence in a rigid system of mineralogy; far lefs in a table. for the use of the public in general, as he has endeavoured to show in the body of his little work.

The additions to the second order are much more

numerous.

The vitreous calcidony, or semi-opal of Mr Born; the sive stone of Rufsia; the adularia from mount Gothard in Switzerland; the iris, a variety of the adularia; the gerasole of the island of Cyprus; the moon stone from Ceylon; the labrador from America and Russia'; the curious green felt-spar of Siberia. The last six, only varieties of felt-spar, and still highly entitled to rank with agates, &c. in the second order, or the word, precious, must be omitted entirely in systems of mineralogy.

The cinate, the thumstein, and crofs stone of Saxony; in fhort the whole genus of horls, in which there are several new discoveries from Siberia and other countries, highly deserving a place in the second order at least.

L

The Venus and Thetis' hair stones of Siberia, the one containing capillary red, the other green fhorl and avanturine from Cape Gate in Spain, the very existence of which stone seems to have been doubted by many naturalists, and its nature unknown to most of the rest. Several more are mentioned in the text

although they do not appear in the column of names, where only such are placed as the author thinks cannot be denied a rank in the clafs of precious

stones.

It would probably amuse, Mr Editor, some of your readers, to give here, at the end of the explanation of the table, a fhort state of the question so often alluded to above, viz. the reasons that have determined systematic writers on mineralogy, to give or refuse a place to certain stones in the two orders of gems.

Anciently, hard stones of the silicious genus, in other respects, of lustre, value, rarity, price, and public estimation, intitled to the appellation of precious stones or gems, might have been placed there without impropriety; but since chemistry has been so ably and properly called in to the aid of the mineralogist, it has been discovered, that the argillacious earth predominates in the composition of the greater number of the finer gems; and some systematic writers would willingly determine the first order by that leading character, which would undoubtedly be convenient and scientific if practicable; but in that case, the diamond, composed mostly of the inflammable principle, joined to an unknown earthy basis in small proportion, must be excluded. The jargon, or adamantine spar, commonly termed the soft diamond, must likewise be excluded, as taking its name, predominates greatly. The aqua marine, admitted likewise by all writers to a rank in the first order, must be rejected by a late analy

a new earth,