NOTES ON ALUNITE, PSILOMELANITE, AND TITANITE. 



Assistant Curator, Dirision of Mineralogy and Petrology. 



A PHOSPHATE-BEARING ALUNITE FROIM TEXAS. 



The material herein described was sent to the United States Na- 

 tional Museum for examination and report by Mr. L. F. Christian, 

 of Lockhart, Texas, the locality being given as " Gonzales County, 

 Texas" (U.S.N.M. Cat. No. 88252). As preliminary examination 

 showed it to possess somewhat unusual composition and properties, 

 it was studied in detail. It has the following properties : 



PHYSICAL PROPERTIES. 



Color: White with very slight yellowish hue; also shows super- 

 ficial brown stains of iron rust. 



Luster : Dull, like chalk. 



Structure: Compact (cryptocrystalline) ; fracture subconchoidal. 



Hardness: 1|. 



Density : 2.67. 



Optical properties : Under the microscope seen to consist chiefly 

 of a fine crystalline aggregate, with occasional grains up to .02 mm. 

 in diameter; colorless; mean refractive index 1.580±:.005; double 

 refraction .005. 



CRYSTALLOGRAPHIC PROPERTIES 



Indeterminate. 



CHEMICAL PROPERTIES. 



Qualitative tests: Before the blowpipe gives reactions for Al, K, 

 Na, SO3, and H.O; in HCl slightly soluble, the solution giving 

 faint reactions for Al and SO3 ; after ignition, H,0 extracts K2SO4. 



Proceedings U. S. National Museum, Vol. 51— No. 2145. 

 36399°— Proc.N.M.vol.51— 16 6 81 



