TmP TO MADAGASCAR LACROIX. 373 



It is necessary first of all to understand what we mean by a precious 

 stone. Mineralogists classify minerals in the first place according to 

 then- chemical composition, then they determine from the form of the 

 crystals how to establish subdivisions of a second order; therefore 

 precious stones are, from every point of view, chemical; a simple 

 element, oxides, alummates, silicates, and many other combinations. 

 AH the modalities that can form crystalline symmetry are found 

 represented there. It is not then the question of a natural family 

 but of an artificial grouping. 



To be a precious stone a mineral must unite a number of qualifica- 

 tions. It must be transparent, of a fine water; that is, very limpid. 

 It should have a strong, clear color; hence, the doubtful tmts, the 

 halftones dear to painters, those which form the charm of certain 

 flowers and the adornment of many animals, are not in favor. The 

 mineral should be very brilliant, which depends upon two optical 

 properties, dispersion and refraction; this last is dependent on den- 

 sity; therefore precious stones are more or less heavy. FinaU}^, it 

 must be hard, so as to take and hold a fijie polish. The more a stone 

 unites these qualities in a high degree, the more readily does it hold a 

 high place in the realm of gems, a place which in addition to this is in- 

 fluenced by its comparatively great rarity. 



To these intrinsic properties of the stone, we should, however, 

 add something exterior to it that escapes the analysis of a min- 

 eralogist, for it is nothing less than feminine fancy, changing ^^dth 

 the fashion. Thus, thanks to the favor which artistic jewels now 

 enjoy, these stones, so correctly caUed "fancy," until lately so 

 neglected, are each day more and more sought after. IMadagascar 

 should not complain, for these are the stones that most of aU adorn 

 her jewel case. 



The definition which I am going to give may be exact; it is not, 

 however, a general one. There are, in fact, some minerals which are 

 neither Umpid, nor clear, nor dense, nor hard, and yet are con- 

 sidered as precious stones. Such is the opaque turquoise, which 

 owes its popularity to its beautiful delicate blue color; such is the 

 opal,^ which takes the charm of its beauty from the warm reflections 

 that play about in its semitransparency. 



A mineral which may constitute a gem, and sometmies of the 

 liighest value, is found not alone in its precious form. At Madagascar 

 even corundum forms transparent sa})phires, the value of which is 

 estimated by the carat of 200 milligrams, and besides some enormous 



I The opal is also found in Madagascar, but it is not yet qtiarriod; in tho phonolito traohyto, coming from 

 the south of Faratsiho, it constitutes very small veins, which possess reflections equal to those of tho opal 

 of Hungary and also some small veins which recall the fire opal, but with a tint more bro^^-n than red. 

 I visited this deposit but collected only small fragments. 



S5360°— SM 1.012 25 



