i 



Prof. B. Silliman, Jr., on some American Minerals. 391 



with its association with corundum, for we find the quality equally 

 developed in the Indianite, (or anorthite,) the Asiatic associate of 

 the same species.* 



Analysis of Indianite. — I thought it of interest in connection 

 with the foregoing analyses to make a new analysis of Bournon's 

 Indianite, which, as already remarked, is found to be the matrix 

 of the corundum in India. Being possessed of an authentic 

 specimen, I requested Mr. Brush to conduct the analysis, the 

 results of which are now given. This mineral is granular and 

 of a pink color, sometimes gray or blackish, very tough and hard. 

 Hardness 7-7-25. Gravity 2-068. It gelatinized completely in 

 cold chlorohydric acid. Before the blowpipe alone infusible. 

 The analysis gave on 1-594 gramme, 



Oxygen. 



Silica, -6710 =perct. 4209 = 21869=4 



Alumina and £ . 6200 « 38 . 89 17 . 160 3 



a trace of iron, 



Lime, ' -2516 " 15-78 4-449 > K RQf? 1 



Soda, -0651 « 408 1-043 J ° Dy/5 l 



1-6077 100-84 



• * ♦ 



• ■ m t • * » 



• Si*R 3 R 3 --R 3 Si4-3RSi 



which is the formula for anorthite. 



VI. On the Boltonite of Shepard, and Thomson's Bisilicate 



of Magnesia. 



The Mineral named Boltonite by Prof. Shepardf is found at 

 Bolton in Mass., in a lime quarry, disseminated in irregular 

 masses, seldom showing any traces of crystalline form. The 

 description of Prof. S. is quoted below.J 



The changes of color are peculiar, and often the same mass 

 which is dark greenish gray on one end, will have turned light 

 yellow on the other. § Hardness 5-50; specific gravity 3-00S 

 the same on two specimens, one dark and one light. 



Dr. Martin H. Boye of Philadelphia, has lately informed me in conversation, that 

 he also made an analysis of this granular albite some time since, and with results 

 closelv accordant to those here given. See Proceed Am. PhiL See. 



t Shepard's Treatise on Mineralogy, New Haven, 1835, vol. i, p. 78. 



t Prof. Shepard's d< ription is as follows—" Massive, composition -ranular : indi- 

 viduals large, cleavage in one direction pretty distinct, in two others oblique to the 

 first, indistinct, but affording indications of a doubly oblique prism fracture uneven 

 or small conchoidal. Lustre vitreous. Color blueish gray, yellowish gray, wax yel- 

 low to yellowish white. The darker colors change to yellow on exposure to the 

 weather. Hardness 5'0-60. Gravity 2*-M* ^ 



m § Mr. Snemann of Berlin, Prussia, in a paper read before ^he Am. Assot for the 

 Promotion of Science at Cambri Igfe, attributes the change of color in Boltonite to 

 minute grains of magnetic iron found disseminated in the substance of the crystal* 

 ^hich, undergoing change by exposure, leave the mineral of a lighter color than it 

 vas when fresh. 



