Mineralogy and Geology. 433 







II. Mineralogy and Geology. 



1. Compact Diamond from Brazil; by M. Dufrenoy, (L'Institut, 

 No. 792, March 7.) — Specimens of compact diamond have been found 

 in the diamond deposits of Brazil. They have the same relation to the 

 crystals as emery to sapphire. One fragment weighed 65*76 grammes ; 

 it had the appearance of a rolled pebble of a brownish color. Under 

 the microscope it appears penetrated by numerous vacuities, separating 

 small irregular lamellae, slightly translucent, and irised in the sunlight. 

 It cuts glass easily and scratches quartz and topaz. The specimens 

 vary in specific gravity from 3*012 to 3-416, being differently porous. 

 They undergo no change when treated in a crucible, showing that they 

 include no vaporizable material. This result does not prove the igne- 

 ous origin of these diamonds, but it renders probable the opinion sug- 

 gested by Liebig, that they proceed from a transformation of vegetable 

 organic matters. By combustion with oxygen they were found to .con- 

 sist of 96*84 to 99*10 of carbon, with 2*03 to 0*27 of ash, the latter 

 being yellowish and appearing like ferruginous clay with some minute 

 transparent crystals whose form was not determined. 



2. Phosphorescence of the Diamond ; by M. Reiss, (Rev. Sci. et 

 Indust., xxiii, 185; Annuaire deCh., 1847.) — The diamond phosphor- 

 escent by exposure to the sun, loses its phosphorescence rapidly when 

 exposed to the red rays ; and on the contrary, in the blue rays, it be- 

 comes most luminous in the dark. 



3. Examination of three new Mineralogical Species, proposed by 

 Prof. C. U. Shepard; by J. D. Whitney, (Jour. Bost. Nat. Hist, Soc, 

 1849, p. 42.) — The species here referred to are the Arkansite, Ozar- 

 kite and Schorlomite from Arkansas, described in this Journal, ii ser., 

 vol. ii, 249, and iv, 279. 



The Arkansite, according to the examinations of Mr. Whitney, is 

 pure titanic acid, with only a trace of iron, (and not a niobate as inferred 

 by Prof. Shepard,) and has the crystalline form and specific gravity of 

 Brookite. His trials make the specific gravity 4*085, Its insolu- 

 bility in acids is strong presumptive proof that it is not titanic acid in 

 combination with a base, since all the known titanates are soluble 

 in acids. 



The Schorlomite was considered by Prof. S. a hydrous silicate of 

 yttria, thorina and oxyd of iron. Mr. Whitney's analyses give the 



following results : 



I. n. in. 



Silica, . . 27-89* 25*66 25*14 



Oxyd of iron with a ) 2V9Q 2V59 , m 



little manganese, ) 



Lime, . . 3005 29-78 . . 



Titanic acid, . . 20-43=100-27 22-10=99-12 ■ , 



making it an anhydrous silicate and titanate of lime and oxyd of 



• •• 



iron, having the formula (Ca 3 Si+Fe Si)+Ca Ti 2 , the first part of 



Some of the titanic acid was not separated from the silica. 

 Series, Vol. VII, No. 21.— May, 1849. 55 



