TURQUOISE: ARTIFICIAL 401 



interest from a mineralogical point of view, since here turquoise occurs in hexagonal prisms 

 some inches in length as a pseudomorph after apatite. 



In Australia turquoise has recently been discovered in the State of Victoria ; no details 

 as to the occun-ence are known, but turquoise has been obtained from a mine called the 

 " New Discovery." 



Artificial Peoduction. — As in the case of all valuable precious stones, attempts have 

 been made to produce artificially a substance resembling the naturally occurring stone, 

 but saleable at a lower price. A certain measure of success has attended these efforts, since 

 there has been produced a mass of which the chemical composition does not differ essentially 

 from that of naturally occurring turquoise, and of which the colour, lustre, hardness, specific 

 gravity, fracture, and general appearance are the same as in that stone. The manufacture 

 is said to be carried on chiefly in Vienna, France, and England : the method adopted is to 

 submit to great pressure a chemical precipitate of the same composition and colour as 

 turquoise. The details of the method are not exactly known, but it would seem that 

 hitherto it has been impossible to produce stones of any considerable size. 



These artificially made turquoises are put on the market together with natural stones ; 

 they are of very good colour, and it is impossible by mere inspection to distinguish them 

 from the turquoise of nature. This being so, the appearance on the market of an unusually 

 large supply of good stones naturally creates suspicion in the minds of possible buyers ; 

 this was the case with a large supply of Persian stones and of the Egyptian or Alexandrian 

 turquoises mentioned above, all of which, however, proved to be genuine. 



Owing to a difference in their behaviour when heated, it is possible to distintmish 

 artificially produced turquoise from the natural stone. The latter, when heated, decrepitates 

 violently and is reduced by ignition to a brownish-black powder, or to a loose mass which 

 easily falls to a powder and does not fuse. The artificial product, on the other hand, does 

 not decrepitate, and on ignition is not reduced to powder, but fuses or runs together into a 

 hard mass, which at least in the interior retains its blue or bluish-green colour ; some or 

 the artificial stones even fuse with moderate ease to a black bead. It is obvious that this 

 method of detection can be adopted only when the complete destruction of the turquoise is 

 of no consequence, as in buying a large parcel of stones, or when it is possible to detach a 

 small splinter from the back of a large stone. It is said to be possible to recognise an 

 artificially produced turquoise from the fact that after lying in water it assumes a darker 

 shade of blue, and on the wet surface can be made out a network of cracks ; moreover, it is 

 said that such stones become softer after immersion in alcohol. There are always to be 

 found adhering to genuine stones particles of the mother-rock, and especially of brown 

 limonite, which is so frequently associated with turquoise ; the presence of such particles 

 was for a long time a sure indication of the genuineness of a stone ; this is not now the case 

 however, for artificial stones are at present furnished with brown specks of hydrated iron 

 oxide in order to imitate natural stones still more closely. 



In the manufacture of artificial turquoise the reproduction or all the essential 

 characters of the natural mineral is attempted, and so similar is the artificial product 

 to the natural stone that it is frequently impossible to distinguish between them except by 

 the employment of special tests. Besides these artificial stones other substances are sub- 

 stituted for turquoise, especially a glass paste, which is made by adding to a mass of glass 

 3 per cent, of copper oxide, 1^ per cent, of manganese oxide, and a trace of cobalt oxide. 

 These paste imitations are easily distinguished from genuine stones ; their lustre is of the 

 ordinary vitreous type, which is not difficult to recognise, especially along the margin of the 

 stone, which is almost invariably splintered during the process of grinding, and where also 



2c 4 



