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



In its granular structure it so resembles dolomite that no differ- 

 ence can be detected between them by the eye, while its hard- 

 ness, and great difficulty of fracture completely blind the enquirer 

 as to its real character. Its characters are as follows : 



Massive, compact, granular, resembling white dolomite ; tough ; 



fracture even but very difficult. Color white with shades of gray. 

 Streak white. Hardness 7-7*25 (scratching quartz with facil- 

 ity). Gravity 2619. 



Insoluble in acids. B. B. infusible and does not color the flame 



• • • • • ♦ 



# Al and Ca. By a 

 quantitative fusion with carbonate of baryta soda was detected. 



The first specimen analyzed was from Lancaster Co., Penn., 

 and showed no trace of corundum disseminated in it. 



This analysis was made by Mr. G. J. Brush and yielded on the 

 quantity taken 1-234 gramme as follows : 



Silica, -8225 = per ct. 66-653 = 34-85 = 12 



Alumina, -2565= " 20786 10-70 3 



Lime, -0253= " 2 050 



Magnesia, -00*1 =•- " 0-519 f- 3-08 1 



Soda, •1155= " 9-360 



12269 99-420 



Oxygen. 



»•* "•■ * ».* #«« - , » • 



ires the constitution Si 4 AlNa=Al Si 3 -f NaSi. 



4 atoms silica = 2309-24= per ct. 69-09 



1 " alumina = 64233 " 19-22 



1 " soda = 390-90 " 1169 



3242-47 10000 



This is precisely the formula and constitution of an albite. 



The second analysis was on a specimen from Unionville, Ches- 

 ter Co , Pa., having identical characters, but associated with corun- 

 dum which occurs implanted in it. This analysis was made by 



Mr. M 



Quantity taken 2-180 gramme. Found 



Oxygen. 



Silica, l-4575 = perct. 66-857 = 12 



Alumina, -4772 « 21-8S9 3 



Lime, -0389 " 1-785 



Magnesia, -0105 " -481 S 1 



Soda, -1914 " 8-779 



Water, -0105 " -481 



2-1860 100-272 



This obviously yields the same formula as the last analysis. 

 The extreme hardness of this mineral is its most remarkable 

 quality and is not easily accounted for. It is probably connected 



