36 HILLEBRAND, MERWIN AND WRIGHT. [April 25. 



Nearly all of our ore specimens from Paradox Valley, Thompson's 

 and the Henry Mountains were free from uranium minerals, but the 

 complexity of the metahewettite ores under special conditions is well 

 illustrated by a very small specimen from Paradox. In addition to 

 constituents indistinguishable to the eye, this showed in juxtaposition 

 and much commingled, metahewettite, carnotite, a brownish material 

 rich in uranium and resembling some forms of ferric phosphate, and 

 jet black, lustrous bituminous or coaly matter. This last, if uranif- 

 erous, is perhaps the unnamed mixture of which a preliminary notice 

 by Karl Kithil appeared in Science^ 38, 62^, 19 13. 



Fortunately several small lumps of very pure material from 

 Thompson's were found. This material gave only a very faint re- 

 action for selenium and was otherwise almost free from contamina- 

 tion. Upon it analysis II. is based. 



Metahewettite crystallizing with 9 molecules of water occurs in 

 two typical habits with intermediate forms. The purest material 

 from Thompson's is a feebly lustrous, loose, earthy powder; that 

 from Paradox Valley appears chiefly in compact aggregates of sep- 

 arable, shining blades, though the earthy variety also is found here. 

 Both are deep red, but on account of the larger size of its bright re- 

 flecting surfaces the bladed variety appears lighter colored. When 

 powdered the bladed variety is claret brown, the earthy variety is 

 dark maroon. The color of the ores containing the mineral varies 

 greatly because of admixed minerals ; furthermore, variation of the 

 water content of the mineral produces changes in color (see p. 46), 



Microscopically the earthy variety consists of minute sharply 

 bounded tables about .04 mm. long, piled in subparallel groups. The 

 outlines and optical properties indicate orthorhombic symmetry. 

 The compact variety consists of plates like those in the earthy variety, 

 closely joined in parallel or radiating, more fibrous aggregates. The 

 optical properties are more easily determined on these large aggre- 

 gates. Pleochroism is strong in groups seen edgewise, but is scarcely 

 noticeable in the plane of the tables, a is light orange-yellow, ^ 

 deep red, y deeper red. Two optic axes barely come into the field of 

 a No. 12 objective over a condenser immersed in oil. 2E thus meas- 

 ured is about 135°. The plane of the optic axes is parallel to the 



