418 Chronicles of Science. [July, 



Kenngott assumes that two minerals are strictly isomorphous if 

 the ratio between the number of atoms of metal and of oxygen is the 

 same in the two compounds. Now, albite and anorthite may both 

 be reduced to the general formula : 4 EO . 6 B0 2 where the ratio of 

 E : = 10 : 16. For our author takes the liberty of writing the 

 formula of albite in this fashion : (Na 2 0, A1,0 3 ) (6 Si0 9 ) ; and that 

 of anorthite in this wise: 2 (CaO. AlO) (2 Si0 2 .A10 2 ). Extend- 

 ing this mode of formulating the silicates, he shows the possi- 

 bility of the existence of a compound containing CaO.Si0 2 -f- 

 AL0 3 . 2 Si0 2 , for such an expression may be thrown into the form 

 (CaO . AlO) (3 Si0 2 . A10 2 ), which is now referable to the general 

 type 2 EO.4 Si0 2 . Such a compound would be, as Tschermak 

 observes, a labradorite free from soda, but we see at once that it is not 

 isomorphous with albite. We forbear to follow Kenngott's interesting 

 suggestions farther, as they lead across the border-land of chemistry. 



In the third number of the new Italian Geological Journal — 

 a journal which we welcome as a fair sign of scientific progress in 

 Italy — Professor Bechi publishes some analyses of minerals from 

 Sig. Foresi's collection.* His examination of some fine limped crys- 

 tals of beryl from the isle of Elba, show that they are remarkable 

 for containing caesium, and for holding more alumina and less glu- 

 cina than other beryls. Traces of lithium were also detected by 

 the spectroscope. A black tourmaline from the granite of the isle 

 of Giglio — an islet rising from the waters of the Tuscan Sea — 

 has also been analysed ; and for the sake of economizing space we 

 place the composition of the two minerals side by side : — 



Tourmaline. 



36-71 .. Magnesia 0-49 



31-57 .. Soda .. 2-83 



8-51 .. Potash .. 0-70 



9-39 .. Boric acid 5*56 



0-64 .. Fluorine 1*85 



Two substances physically distinct, but occurring together near 

 Brevig in Norway, have hitherto been confounded under the general 

 name of Esmarhite. One of these is a true Praseolite, but the other 

 is an extremely rare mineral, which has received Des Cloiseaux's 

 attention during his visit to Norway.! This acute crystallographer 

 has carefully examined authentic specimens of the true Esmarkite, 

 and pronounces it to be merely a laminar variety of the felspar — 

 anorthite. 



Several new species recently described demand a cursory notice. 

 Glaucopyrite is Professor Sandberger's name for a new mineral, ob- 

 tained from Guadalcanal in Spain, and consisting of an arsenio- 

 sulphide of iron, in which part of the iron is replaced by cobalt and 



* "Analisi chimiche di alcuni minerali delle t isole del mare toscano." — 

 ' Bollettino del K. Comitato geologico d'ltalia,' 1870, p. 82. 

 t * Ann. d. Chim. et de Phys./ 1870, p. 176. 



Silica 



Beryl. 



. 70-00 

 . 26-33 

 . 3-31 

 . 0-88 

 . 0-42 



Silica 



Alumina 

 Glucina 

 Caesium . 

 Oxide of 



uron 



Alumina 

 Ferric oxide 

 Ferrous oxide 

 Lime . . 



