GEOLOGY. 273 



Shepherd has given the name boltonite, is identical with sphene. 

 The bisilicate of magnesia of Dr. Thompson, also found at Bolton, 

 is hornblende, variety actinolite. 



The sillimanite of Bowen, the bulcholzite of Brandes, the fibrolite 

 of Bournon, Prof. Silliman shows to be but varieties of the well- 

 known mineral kyanite. Prof. S. remarks, " that andalusite has 

 the same chemical constitution as kyanite, but belongs to the right 

 rhombic form, while kyanite is oblique. Doubtless it is a case of di- 

 morphism, and perhaps the same may be said with truth of stau- 

 rotide." 



ON THE OCCURRENCE OF RARE MINERALS IN THE UNITED 



STATES. 



Mr. J. E. TESCHEMACHER, in a paper recently read before the 

 Boston Society of Natural History, showed that the mineral called 

 arkansite by Prof. Shepard, recently discovered in this country, is 

 identical with the brookite of European mineralogists. Brookite is 

 oxide of titanium, with traces of iron and manganese, and has 

 hitherto been so extremely rare as to have been only analyzed by 

 Prof. Rose, of Berlin. It occurs in this country in considerable 

 abundance. 



Dr. C. T. Jackson, of Boston, has also found associated with some 

 gold ores from Virginia, the rare mineral tellurium, in the form of 

 a telluret of lead and gold with a little silver and a small amount of 

 selenium. These minerals, tellurium and selenium, have never been 

 found before in America. With some of the specimens Dr. Jackson 

 has also found bismuth, a rare combination. 



NETV ADAMANTINE MINERAL. 



M. DUFREXOY exhibited before the French Academy, in March, 

 a specimen of a mineral from Brazil, which appears to be to the 

 diamond what emery is to corundum. Among some specimens sent 

 to the ' ; Ecole des Mines" by a dealer in minerals were two, which 

 were stated to be hard enough to polish the diamond ; and, in fact, 

 they were found to be harder than topaz. This substance was an- 

 alyzed by M. Rivot, who had at his disposal one large fragment and 

 several smaller ones. The large fragment appeared to come from 

 the same alluvial formation as that in which the Brazilian diamonds 

 occur. Its edges are rounded by long friction, but it has not the ap- 

 pearance of a rolled flint. It is of a slightly brownish, dull black 

 color, and when viewed with a glass it appears riddled with small 

 cavities, separating very small irregular laminae, which are slightly 

 translucent and iridescent. The brown color is very unequally dis- 

 tributed throughout the mass, and on the faces the cavities are linear, 

 which gives it a fibrous aspect similar to obsidian. It cuts glass 

 readily, and scratches quartz and topaz ; its density is only 3.012, 

 while the smaller specimens are respectively 3.141, 3.416, and 3.255. 

 These numbers indicate a great difference in the porosity of the speci- 



