384 Prof. B. Silliman, Jr., on some American Minerals. 



I have had no means of comparing the optical properties of 

 these several minerals. The angle between their axes of polar- 

 ization should be measured to ascertain if the differences shown 

 in their composition are found also in their molecular structure. 

 When we review the characters of the minerals here described, 

 we are struck with the almost identity of all their ordinary phys- 

 ical characters, and yet there are differences which are apparent 

 especially in their composition. It therefore becomes an inter- 

 esting question to decide if the optical characters will sustain the 

 chemical results. The occurrence of a class of salts with such 

 a very small amount of protoxyd bases, and so large a content 

 of alumina as these possess, is a novelty in the chemical his- 

 tory of minerals, and may have some important theoretical con- 

 nections. Our knowledge of the whole mica family is quite im- 

 perfect at present. The true function of the fluorine found in so 

 many of them yet remains to be explained, and especially is it of 

 the greatest importance that a careful series of optical measure- 

 ments should be made on authentic specimens from numerous 

 localities, and at the same time an exact series of chemical analy- 

 ses conducted on specimens from the same localities. 



Mineralogy hardly offers a more inviting investigation than 

 this, and should it not fall into better hands, it will at a future 

 day be attempted in this Laboratory. 



II. On Untonite. 



The next mineral to be noticed is from the same specimen 

 which furnished me the Eiiphyllite. In general appearance it 

 somewhat resembles scapolite or spodumene. It is implanted in 

 black tourmaline, and is intimately associated with the eiiphyllite. 

 Its form is discernible only by its cleavages which are distinct in 

 one direction, the planes dividing the mineral into parallel laminae, 

 in two other directions less distinct, but yielding a form probably 

 triclinate.* Lustre vitreous. Color yellowish white to white. 

 Hardness 6-6-5. Gravity 3 2984. Brittle, and easily reduced to 

 powder. In acids does not gelatinize. 



B. B. In forceps it whitens, swells up and fuses to a white 

 enamel, giving out at the same time an extremely brilliant light 

 In the matrass it gives out water which is acid, and the glass is 

 etched with fluo-hydric acid. Qualitative analysis detected silica, 

 alumina, magnesia and soda. The amount of water was deter- 

 mined by the loss on heating, and the fluorine was not separately 

 estimated. In the quantitative analysis the mineral was attacked 

 by carbonate of baryta. 



The following are the results of analysis. 



# 



The angles do not admit of measurement. 



