268 Notice of some Recent [April 



7. Humboldtilite. — Kobell finds this mineral composed of 



Silica 43-96 



Alumina . . . . 11*20 



Lime 31*96 



Magnesia ... 6*10 

 Protoxide of iron . 2*32 



Soda 4-28 



Potash .... 0-38 



100-20 

 and itsformulais5Al.S + 9CS + 3(| M + { F) S 2 + NS 2 



8. Phenakite from Ural. — Colour yellow, or like quartz. 

 Sp.gr. 2-969 ; crystals rhombohedrons. The angle of the 

 rhombohedron is very obtuse, being, according to measure- 

 ment by the common goniometer, 114°. Colour, none. 

 Before the blowpipe it does not fuse per se. Fuses with 

 difficulty with borax, and salt of phosphorus. It is found 

 in Siberia, and has received its name from its resemblance 

 to rhombohedral quartz, (fcmi; deceiver.) Hardness greater 

 than quartz, but less than topaz. It contains 



Silica .... 54-54 

 Glucina . . . 45*46 



100-00 (Poggendorff Ann.) 



9. Magnesia, — protoxide of iron — A mineral thus consti- 

 tuted has been described by Breithaupt. (Jahrbuch. vi. 

 1833.) It is brought from N. America, and is accompanied 

 with uraniferous spinelle. The crystals are imperfect octa- 

 hedrons ; cleavage uneven and slightly conchoidal ; lustre 

 semi-metallic; colour deep greyish black, slightly mag- 

 netic; sp. gr. 4-418—4-420. 



Before the blow-pipe infusible, per se. With borax it 

 behaves like the tetaniate of iron. It consists of protoxide 

 of iron, much magnesia, a notable quantity of tetanic acid, 

 and a little alumina. 



10. Junclterite. — The crystals of this mineral, according 

 to Dufrenoy (Ann. des Mines, vi. 273. J are rectangular oc- 

 tahedrons, with nearly equal faces. Two of its cleavages 

 are parallel to the diagonal planes of the octahedron, and 



