Prehniie. — Olivine. 2?3 



" This mica has a beautiful rose-red colour, and occurs 

 near Penig, in Saxony, together with amblygonite, topaz, al- 

 bite, schorl, &c. 



" Most of the minerals that occur in this place contain li- 

 thion; as for instance, a fine variety of quartz, lithomarge, 

 andalusite, &c. I shall publish the analyses of all these mi- 

 nerals in the Edinburgh Philosophical Journal, and it will give 

 me much pleasure to send you specimens of each. 



"While on this subject, allow me to say that I have discovered 

 a very useful test for lithion, before the blowpipe; viz. the flame 

 assumes a very fine purple colour, — but the flame of an oil 

 lamp should be used, and not that of a tallow candle. By 

 means of the latter the colour of the flame is not so decided. 



" By an analysis of Helvin, a very scarce mineral, I have 

 discovered glucine to be a constituent of it. It consists of 



Silica 33-258 



Glucine 12-089 



Oxydule of manganese 31-817 



Protoxide of iron S-Se* 



Sulphuret of manganese 14-000 



96-728 

 Loss by ignition 1-555 



" The Latrobite of Mr. Brooke (diploite of Bresthaupt) is 

 composed, according to my analyses, of 



Silica 44.-653 



Alumina 36-814 



Lime 8-291 



Ox. of manganese 3-160 



Manganese with ox. of manganese . . 0-628 



Potash 6-575 



100-000 



Gain -121 " 



Letter from Prof. Gmelin to Dr. Van Rensselaer 

 ill SiUiman's Amer. Jowm. 



PREHNITE. — OLIVINE. 



A very elaborate examination of several varieties of prehnite 

 has been made under the direction of L. P. Walmstedt, pro- 

 fessor of chemistry in the university of Upsal, by MM. P. F. 

 Wahlberg, J. A. Hoeger, and S. A. Varenius, candidates for 

 the philosophical degree. The very discordant results ob- 

 tained by the diflerent chemists who had analysed this mhieral, 

 induced these gentlemen to make it the subject of their ex- 

 periments. 'I'he analyses of two varieties of prehnite made by 



Gehlen, 



