9 % 2 Hjdrophaneoiis Stone, &c. [Book VI, 



Hire of the hydrophanous {tone, which is opake when 

 dry, but gradually acquires tranfparency by lying in 

 water. This flone agrees nearly in fpecific gravity 

 v/ith water, at leaft is not more diftant from it than 

 glafs. Its particles are tranfparent, but it is uniformly 

 perforated by invifible foramina, fo that the air and 

 water are admitted, but not readily. When dry, 

 therefore, on account of the great difference of the me- 

 diums between the particles of the (lone and thofe of 

 the air, it is opake ; but when the water is gradually 

 imbibed, it grows by degrees pellucid, beginning at the 

 furface, and proceeding towards the center. That 

 tlie hydrophanes abforbs moifture and emits air, 

 v.hich is a fluid of ranch lefs denftty, appears from 

 the weight it acquires, and the fmall bubbles which 

 cover its furface during the time it is acquiring its 

 tranfparency. 



4. Moon-done, or rainbow-ftone, refkfts light of 

 pearl and carnation colours. Its fracture is foliated, 

 and its colour pale blue and milky. 



5. Chalcedony, or white agate. This ftone is 

 ufually cut with a convex furface, and receives a good 

 polifh. Its degree of hardnefs is intermediate, be- 

 tween that of the onyx and the true agate. It is fe- 

 mitranfparent, and its colour is ufually very fimilar to 

 that of milk diluted with water. 



6. The onyx is the hardeft of flints. Its ufual colour 

 is that of the human narls. It is either marked 

 with white lines only, or with black and white toge- 

 ther. Heat deprives it of colour, and, if fuddenly. 

 applied, cracks it. 



7. The carnelion derives its name from its refem- 

 blance to the colour of flefh. It is either quite red or 

 of different fnades of red, with brown and yellow. . 



$. The fardonyx is a mixture of the chalcedony and 



carnelion. 



