Ml NERALOGY, 6 S 



SECT. LVII; 



3; The Onyx. Onyx Camelwja. Memphites. 

 This' ilone is the -hardeit of the' flinty- 

 tribe, and conlifts of differently coloured 

 veins, which run parallel' to one another, 

 fometimes in ftraight, fo metimes in curved 

 lines. It is found of two forts. 



a. Nail-coloured onyx', having; pale" flefh- 

 coloured, and white lines.. From the 

 river' Tomm in Siberia. 



b. With black and white lines. The Oriental 

 onyx. 



The old Romans were -acaiflorned to 

 cut figures on theltraight-lineci onyxes in 

 relief, which they calkd Camebiija -, thefe 

 are frill counterfeited, and called Cama- 

 yeu. Thofe which confift of concentric 

 circles were caned Memphites ; and we 

 have now of this kind cut to be fet in 



ing been laid in water, mines like a piece of red-hot charcoal; 

 the Afteria, which is laid tc fnew luminous liars on its furface, 

 &c. Buc thefe are no longer to be met with, fince fafliion 

 has given prci-rcnce to the more tranfparent hard ftones ; 

 and it is alfo very difncu't rightly to understand the-defcrjp- 

 tions of antient authors, in regard to colours, and their dif- 

 ferent mixtures with one another J. 



k>.d the beginning is round the edges) which increafes by How decrees 

 until the whole itone is become uniformly clear throughout : when 

 tiken out of the water, it lofts its tranfparency, firffc at one end, 

 thsn gradually over the rem:iir>der, until the whoie ft^ne has recovered 

 Drmer opacity ; and this change happens in iefi time than that of its 

 h-comim* tranfparent. No other experiment* have yet been made 

 upon this ftone, becauft it is fo very feldom to be met with ; and thefe 

 are not fufneient to determine exactly of what kind it is. E. 



X Arncngft thefe cannot be reckoned the Tourmaline, fo much re- 

 nowned of la'e for its electrical qualities. It is but a cryftailifed cockle 

 of a green or brown colour, more or lefs deep, fo as to turn to a 

 Hack, an-! fometimes to a bluifh colour, when looked through : others 

 \x quite black. [See Se£r. LXXV.) E. 



Brafilian erneraid feerns to have the fame properties of becoming 

 electrified pofitively in one fide, and negatively in the othef < it belongs 

 . be Shirl kind. [See Seel. XLVIII. Notef I 



F rings, 



