374 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. XIII 



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1. Chrysolite. 



The globular-shaped bodies which compose the chief part of the Virginia aerolite are thus denominated, because 

 in their mineralogical characters they approach very closely our species of chrysolite. I offer the following description 

 of its characters: 



External shape spheroidal, or subangular. 



Structure lamellar, cleaving in two directions; at right angles to each other, or as nearly so as the perfection of the 

 planes will allow us to observe. One of these cleavages is effected with greater ease than the other and presents imper- 

 fect horizontal striae. The lamellar structure is often interrupted by a subconchoidal fracture. 



Luster vitreous and splendent in the most perfect cleavable masses, but glimmering only on the conchoidal surfaces. 

 Color gray, often with a tinge of blue, and rarely olive green. Translucent on the edges, and in a few instances trans- 

 parent. 



Hardness equal to that of crystallized adularia, the one impressing the other only when great mechanical violence 

 is exerted. It scratches the crystallized pyroxene of Mussa. 



Specific gravity was determined upon a mass, which before its fracture into two pieces, weighed 6.1 grams; the entire 

 mass gave 3.3 and the largest fragment 3.33. Another mass weighing 3.4 grams gave a specific gravity of 3.90. The 

 mean of the three experiments is 3.259. 



Chemical examination. Before the blowpipe, in small fragments, with the most intense heat that could be urged, it 

 fused with ebullition upon its thinnest edges into a shining black glass, and the fragment became immediately attracted 

 by the magnet. With borax, in powder, it dissolved, forming a greenish transparent glass. With carbonate of soda it 

 entered into fusion with difficulty, becoming transparent or nearly so in the full heat of the blowpipe, but immediately 

 turning dark-reddish brown and becoming opaque, on being removed from the flame and finally changing to white. 

 With microcosmic salt it dissolves with readiness and the glass assumes a deep straw-yellow color which on cooling 

 becomes a paler tinge and contracts a degree of cloudiness. 



******#** 



Analysis. A. 17.8 grams reduced to powder were mingled with double their weight of potash and 10 grams of 

 nitrate of potash. The mixture was kept at a red heat in a silver crucible for one hour. The calcined mass which had 

 evidently undergone fusion presented a yellowish-green color which it communicated to its solution in water. On the 

 addition of nitric acid the fused mineral became perfectly soluble, with the exception of a few white flocculi of silex 

 which were seen floating through the solution. 



B. The nitric solution was evaporated to dryness, in which state it was kept at a heat of 212 for upward of half 

 an hour to ensure the complete decomposition of the nitrate of iron and the separation of the silex. The dried mass, 

 which was reduced to the state of a powder and frequently stirred, assumed throughout a deep reddish-brown color. 

 Warm water was now affused and the oxide of iron and silex separated by means of the double filter. 



C. This solution (B), reduced by evaporation to a convenient bulk, was boiled for upward of an hour with an excess 

 of carbonate of soda. The precipitate which ensued was washed, dried, and heated to ignition in a platina crucible 

 for twenty minutes, after which its weight was 5.5 grams. Its color was pure white, and upon the addition of dilute 

 sulphuric acid it was wholly taken up with the exception of a few flocculi of silex whose weight it wSs not attempted 

 to ascertain. The solution was partially reduced by evaporation and set aside to crystallize. In two days it shot into 

 crystals of Epsom salt. 



D. The insoluble oxide of iron and silex (B) was heated to redness in a close platina crucible over an alcoholic 

 lamp, after which they weighed 11.62 grams. The mixture was now digested with hydrochloric acid until the oxide 

 of iron was wholly dissolved ; the silica remained behind in white flocks, and was separated by the double filter, washed, 

 dried, and ignited. Its weight was 7.53 grams. This amount deducted from 11.62 grams gives 4.09 grams peroxide of 

 iron, which reduced by calculation to the protoxide, the condition in which it probably exists in the mineral, equals 

 3.68 grams. . 



The constituents of this mineral, therefore, appeared to be in this instance 



Silex ,. 7.53 



Magnesia 5. 50 



Protoxide of iron 3. 68 



Soda, oxide of chrome, sulphur, and loss 1. 09 



17.80 

 or per hundred 



Silex 42. 30 containing oxygen 21. 27 



Magnesia 31. 46 containing oxygen 12. 17 



Protoxide of iron 20. 67 containing oxygen 4. 59 



Soda, oxide of chrome, sulphur, and loss 5. 57 



100.00 



Considering the soda and oxide of chrome as accidental, the preceding analysis, it will be observed, agrees very 

 well with the supposition that the present variety of chrysolite is a compound of one atom bisilicate of iron, with three 

 atoms silicate of magnesia, and its coincidence with the mineralogical formula fS 2 +3MS will be still more striking, if 

 we suppose the oxygen of the iron is estimated a little too high, in consequence of the probable union of a small portion 



