THE GEOLOGIST. 



65 



FOREIGN COERESPONDENCE. 

 By De. T. L. Phipson, of Paeis. 



The Emerald and its green colour — Its analysis and formation — Green 

 Gyp-mm in the Emerald mines — More artificial minerals — Syalite^ 

 Wollastonite, and Aphophyllite — Quartz, Feldspar, and Pyroxen — 

 Feldspar in the lava of volcanos — Petrifaction and Epigenesis — 

 Spontaneous crystallisation of amorphous bodies — Hardening of rocks hy 

 eayposure to the air — Extraordinary origin attributed to oolite rocTcs — 

 Modern oolite discovered by Leopold Von Buch — More Footprints in the 

 Jurassic formations. 



One of the most interesting results has just been obtained by a 

 thorough chemical investigation of the emerald. This interesting 

 fnineral, which has given rise to so much discussion as to its composition, 

 its formation, its colouring matter, &c., may now be looked upon with 

 still greater interest since the researches of M. Lewy have been made 

 known. The ingenious chemist just named, in a visit to the mine 

 called Muso, in New Grenada, Mexico, was lucky enough to procure 

 some very fine specimens of emeralds, and of the rock in which these 

 precious stones are found. The first thing that struck him, on receiving 

 these specimens from the hands of the miners, was the excessive 

 fragility of the stones : the largest and finest emeralds could be actually 

 reduced to powder by a slight squeezing or rubbing between the 

 fingers. 



It is a well-known fact that the ancient inhabitants of this part of 

 America used to judge the value of the emerald by its hardness. So 

 little had they observed the phenomenon of which we speak, that 

 their principal test consisted in striking a hard blow upon the stones as 

 soon as they were extracted from the earth : if they resisted they were 

 considered perfect stones, if not they were thrown aside as valueless 

 articles. M. Bousingault remarks that in this manner, no doubt, a 

 great number of very valuable specimens have, in former times, been 

 destroyed. 



A certain space of time and repose are required for these soft emeralds 

 to assume the hardness which renders them valuable as precious stones. 

 The fine specimens destined for the lapidary and the jeweller must be 



