164 PROCEEDINGS OF THE ACADEMY OF [1889. 



GADOLINITE FROM LLANO CO., TEXAS. 

 BY E. GOLDSMITH. 



The specimen so called which came from the above locality is in 

 the Wm. M. Vaux Collection of the Academy and is of unusual size. 

 It appears as a rough orthorhombic crystal. A piece broken off at 

 one end revealed the fact that the crystal was not homogeneous 

 throughout. Within, a glassy material surrounded by a rather thick 

 layer of perfectly dull appearance indicated that it was made up of 

 at least two different minerals. I procured from the mineral dealer 

 fragments of these two substances for investigation. The inner or 

 vitrous substance proved to be Gadolinite. In mass the color is 

 deep black and opaque but, when a thin plate is prepared by grind- 

 ing, it appears green. Beneath the microscope apparently all is 

 homogeneous, only a few minute black spots are noticed. Between 

 the two nieol prisms it was not at all affected, even when the ray 

 passed through it parallel or convergent. The field of the crossed 

 nicols became darker when the plate was placed between them. 

 The apparent form is therefore misleading. Supposing the optical 

 laws of crystallized bodies to be correct, I arrive at the conclusion 

 that the crystal found is either isometric or pseudomorphous. 



Fracture conchoidal and uneven. Hardness = 6. Sp. Gr. = 

 4*276. It affords no streak on unglazed porcelain and it is brittle ; 

 the powder is grayish-green. 



For analysis the substance was selected with care and was easily 

 decomposed by hydrochloric acid, the silica gelatinizing. 



The result was as follows : 



Silica 25-70 per cent. O = 13-7 



Ittria 58-30 " " = 12 



Iron monoxide 15*52 " "= 3*44 



Glucina 2-10 " " = 1*32 



The oxygene ratios of the silica to the monoxyds is as 1 : 1*2, 

 therefore nearly 1 : 1 which corresponds fairly with one of Berlin's 

 analysis of material from Ytterby, except that he found in all his 

 investigations cerium, small quantities of alkalies and alkaline 

 earths. I took special pains to trace the presence of cerium but 

 could not detect it. The ittria found was dissolved as nitrate and 

 the concentrated solution examined spectroscopically for erbia, but 

 none was found. I confess to not knowing a reliable process for 



