Some Remarks on the Precious Stone Called the Turquoise; By Cromwel Mortimer, Sec. R. S. &c.

scended a great many times. I thought, at first, it had spun a new Thread at every Descent, and was desirous to have measured how long an one I could cause it thus to spin; but, upon a stricter Examination, I very plainly perceived, that whenever it ascended, it wound its Thread with its Feet into a sort of Coil, and when it descended only ravelled it out again. The Manner how they perform this is diverting enough; but as Spiders may be had almost in every Place, and the Experiment is so easily tried, I shall forbear describing it; and only add, that as these Coils of Thread are exactly like those floating in the Air towards the End of Summer, I think it is not improbable those are made in the same Manner, when Spiders have a Mind to direct their Course in the same Direction their Threads lie. XVII. Some Remarks on the precious Stone called the Turquoise; by Cromwel Mortimer, Sec. R. S. &c. Read Feb. 26. 1746-7. THIS Stone has received its modern Name of Turchesia, and Turquoise, from its being most commonly brought from Turkey into various Parts of Europe. De Boodt * says, the Colour of this Gem is a Variegation of Green, White, and Blue; and that there are two Sorts of it, the oriental, from the East Indies and Persia, and the occidental, * Gemmar. et Lap. Hist. occidental, from Spain, Germany, Bohemia, Silesia, &c.; that in Persia, where it is found in greatest Plenty, it adheres to black Stones, as if it were an Excrement or a Transudation from them. A Stone of this sort is seldom found to exceed a Walnut in Size; and he mentions one in the Great Duke's Museum, on which the Head of Julius Caesar is engraved, as a very extraordinary Sample: He adds, That he never saw one bigger than an Hazel-nut; that some of the oriental ones have the Faculty of preserving their Colour perpetually, which are called Stones of the old Rock; and that others lose their Colour gradually, and are called of the new Rock. He then gives an Instance of a Turquoise which had lost its Colour upon being laid by some time after its Owner's Death, which recover'd its beautiful Colour upon our Author's wearing it upon his Finger in a Ring. Cæsius, in his Treatise de Mineralibus, p. 601. says, This Stone is called Turcoïs by Mylius, in his Basilica chemica; by Albertus Magnus, in his Treatise of Minerals; and by Rueius, in his Treatise of Gems: but Turca, by Caussinus de Lapillis symbolicis. De Boodt, and Dr. Woodward,* with other modern Writers, take it for the Callais of Pliny. Salmasius, in his Plinian. Exercit. p. 142. says, Many have mistaken the modern Turquoise for the Cyanus, but that the Cyanus was transparent like the Saphire; whereas the Turquoise is a sort of Jasper. Dr. Woodward, in his Letter to Sir Jo. Hoskyns,† says, That the Turcoïs, or Callais of Pliny, is nothing else but fossil Ivory tinged with Copper. I * Method of Fossils. Letters, p. 17. † Ibid. p. 16. do not deny, that some Stones sold for Turquois, and possibly all that the Doctor saw were certainly such; but I imagine those which the Authors call of the old Rock, and in which the Colour is permanent, are real mineral Stones: This Sample now before us seems to shew this, from both the Form and Size: Its Shape shews it not to be Part of any animal Bone; but its botryoid Form is to me a Demonstration that it is the Product of Fire, which had once melted this Substance; and that when it cool'd, its Surface was formed into Bubbles and Blister, in the same manner as the Hematitis botryoides or Bloodstone, whose Surface consists of Knobs, resembling a Bunch of Grapes. That the Elephas ἐποχής, or Ebur fossile of Theophrastus*, said to be of various Colours, I do not in the least deny to be tinctured with Copper, and to be what Dr. Woodword calls the Turquois: Indeed I suspect it to be what De Boodt calls of the new Rock; and says is liable to lose its Colour, which it recovers again from the Effluvia of the Person who wears it. I therefore, for Distinction sake, think all these Stones of the Ivory Origin should be called Pseudo-Turchesia, or bastard Turquois; and the other Sort, of which this before us is one, the true or real Turquois; for, by Examination in the chemical Way, I find it to be a very rich copper Ore; some of it pounded and dissolved in Spirit of Hartshorn gives a deep Blue; in Aqua fortis a fine Green; and an iron Wire put into it was in 1 Hour's time incrusted with Copper: Some of it calcined, without any Flux in a Crucible, run * See Theophrastus's Hist. of Stones, translated, &c. John Hill, Lond. 1746. 8°. p. 94. to a Slag, or half vitrified Substance; whereas the same Heat, had it been Ivory or Bone, would have reduced it to a white Ash like Bone-Ashes; for I exposed it to such a Fire as vitrified the Tile that cover'd it. Its Hardness and Consistence to an Engraver's Tool seems to be the same as common white Marble: Its Colour is not mended by Heat, but it grows brittle when red hot. This Specimen, now shewn to the Society, was about 12 Inches long, 5 Inches broad, and in some Places near 2 Inches thick; rough on the under Side, as though broken off from the Rock it had been affixed to; and the upper Side was composed of smooth polished Knobs, in Form like to the botryoid Iron Ore. Sir Hans Sloane, in his noble Museum, has several Specimens of these oriental Turquoises, all botryoid; especially a Mass from China, about three Inches long, two broad, and near an Inch thick: All which seem to be Copper Ores: And he has likewise Samples of Turquoises from Spain, and the South of France; which are all small, and seem really to be Pieces of Ivory tinged with Copper. XVIII. A Description of a curious Echinites; by Mr. Henry Baker, F. R. S. Read Feb. 26, 1746-7. Mr. Baker takes the Liberty of shewing the Society a very extraordinary Echinites, the like to which he has never seen in any Museum, or found described by any Author. For the Echinite usually met with, are made up either of Chalk are Flint, or some stony, chalky, or sparry