174 



A. O. Des Cloizeaux on 



[Feb. 20, 



II. " On a new Locality of Amblygonite, and on Montebrasite, a 

 new Hydrated Aluminium and Lithium Phosphate.'''' By A. O. 

 Des Cloizeaux. Communicated by Prof. W. H. Miller, 

 Foreign Secretary U.S. Received November 27, 1871. 



(Abstract.) 



A mineral found in 1862 at Hebron, Maine, IT. S. A., after a mere 

 tentative examination by Professor Brush, who announced the presence 

 in it of lithia in considerable quantity, resembled the amblygonite of Penig 

 so closely as to lead to its being looked on as amblygonite. The crys- 

 talline system and birefringent optical characters of this mineral were 

 determined by the author in 1863. In 1870 a mineral found in the tin 

 vein of Montebras (Creuse), though resembling the amblygonite of Hebron, 

 appeared to the author to differ from it so far as to justify his designation 

 of it under the name of Montebrasite. Towards the close of 1871 he 

 received another specimen from Montebras, which presented all the cha- 

 racters of the American amblygonite, and which consequently was easily 

 distinguished from the montebrasite. Subsequently, analyses by Pisani, 

 v. Kobell, and Bammelsberg, and optical observations by the author, 

 proved the identity of the montebrasite of Montebras with the ambly- 

 gonite from Penig. But this is not the case with the amblygonite from 

 Hebron, nor with that from Montebras, which had been analyzed by Pisani. 

 These differ from the amblygonites of Saxony and Montebras (which last he 

 had previously named montebrasite) by the absence of soda, by the pre- 

 ponderance of lithia, and the presence of a notable amount of water, while 

 at the same time they contain almost equal proportions of phosphoric acid 

 and alumina. 



The differences which these two minerals present in their physical and 

 chemical characters are sufficiently decided to compel our treating them 

 as distinct species. The name amblygonite should be retained for the 

 sodolithic species first discovered at Penig by Breithaupt, and the white 

 or violet-tinted lamellar masses abundant at Montebras will be included 

 under it ; the hydrated and entirely lithic species comprising the laminar 

 specimens and the crystals from Maine, as well as some greenish masses 

 from Montebras, should be embraced under the name montebrasite. 



The amblygonite of Montebras has only been met with in laminar 

 masses with a faint tinge of violet. These masses exhibit two cleavages 

 presenting nearly the same degree of facility, making with one another 

 an angle of 105° 44'. Close observation shows that the sharpness of the 

 reflected images is generally a little greater on one of the cleavages 

 than on the other ; and this induces one to suppose that they do not both 

 belong to equivalent crystallographic planes. The study of some of their 

 optical properties, though presenting certain special difficulties, arising 

 from the small extent of the transparent portions and the presence of 



