Thoria Minerals from. Llano County, Texas. 485 



elude that the water is not present as water of crystallization, 

 but as hydroxyl which is partially replaced by the fiuorine, and 

 this being so we consider that the name fergusonite should be 

 reserved for the anhydrous mineral, and that the various defi- 

 nite alteration products with two, four, six and perhaps more 

 hydroxyls should be distinguished in some manner either by 

 prefixing mono-hydro, di-hydro, etc., or by special names. It 

 seems better that the first method of distinguishing them 

 should be followed. We believe that we have observed a still 

 higher alteration product in traces on some of the specimens 

 we have obtained from Texas. 



Allan ite, has not as yet been found very abundantly at 

 this locality and all of the ten kilos obtained was massive- 

 nodular in form. Its surface alteration is very slight compared 

 with that of the other allied minerals. Its color is shining 

 pitchy-black. Powder and streak dull greenish-brown. Upon 

 ignition it first turns red-brown and then becomes coal-black. 

 It is opaque, except in the very thinnest splinters, when a 

 greenish-brown translucence is evident. Specific gravity = 

 3488. We have made no complete analysis as yet, but the 

 specimen tested showed the presence of considerable quantities 

 of the cerium-yttrium earths and of thoria, and we learned 

 that it was completely soluble in acids with separation of 

 gelatinous silica, either before or after igniting the mineral 

 (like the associated gadolinite). The better masses have been 

 found quite isolated from the other occurring minerals. 



Molybdenite, occurs sparingly in quite large folia, and in 

 hexagonal tables, with the cyrtolite and fergusonite. Only a 

 few ounces have been collected. 



Moltbdite, was noticed in the cavities once occupied by 

 molydenite and it often yet retained the plate-like form of the 

 mineral from which it was derived by alteration. Its color was 

 white to greenish-white. Specific gravity = 4 , 004. On two 

 specimens indistinct crystals have been found, having a light 

 apple-green color and almost perfect transparency. Qualita- 

 tive tests have shown the absence of any large amounts of any- 

 thing but molybdic acid. 



Ctrtolite, has been found abundantly in both massive form 

 and in good crystallizations. One hundred kilos have thus far 

 been collected while mining the yttria minerals already herein 

 described. This mineral here occurs in thick plates attached 

 to the biotite and also constituting veins in the coarse pegma- 

 tite. It is often the matrix of the thoro-gummite and fergu- 

 sonite. Specific gravity = 3*652. It occurs in tetragonal 

 forms with all the planes rounded, and polysynthetic group- 

 ings of crystals are very common. Its color ranges from dull 

 gray, through various shades of brown to deep brown and 



Am. Jour. Sci.— Third Series, Vol, XXXVIII, No. 228.— Deo., 1889. 

 31 



