488 T. L. WATSON WEATHERING OF ALLANITE 



In 1878 analyses were made by Santos of the weathered product (crust) 

 of allanite from Little Friar Mountain, Amherst County, Virginia, in- 

 cluding a separate analysis each of (a) the outer white layer and (h) the 

 inner red layer. Comparing these analyses of the weathered product with 

 an analysis made of the fresh mineral from the same locality by CabelF^ 

 in 1874, Santos briefly called attention to the chemical changes incident 

 to the weathering of the allanite. Later (1885) Valentine^* analyzed the 

 weathered crust of allanite occurring near Lowesville, Il^elson County, 

 Virginia, and in 1885 an analysis of the fresh mineral from the same 

 locality was made by Memminger;^^ but a discussion of the chemical 

 changes involved in the weathering of the mineral was not published. ', 



• i 



\ ROANOKE COUNTY \ 



Locality and mode of occurrence. — The allanite locality^*^ in Eoanoke 

 County is a new one and is described here for the first time. The mineral 

 occurs on that part of the Shepherd farm located on the crest of the Blue 

 Eidge Mountains, in Eoanoke County, within a few paces of the Franklin 

 County line and in a direct line about 9 miles south of Eoanoke City. 



The allanite occurs as a constituent of a pegmatite body exposed by a 

 small pit opened to a depth not exceeding 10 feet. Both the pegmatite 

 dike and the inclosing rock are greatly weathered. Because of this fact 

 it was not possible to measure the dip, strike, and width of the pegmatite. 

 So far as could be determined by the opening made, the allanite is dis- 

 tributed irregularly through the pegmatite, but in quantity as grains and 

 masses up to many pounds in weight, and to some extent in stringer-like 

 bodies. A specimen of the massive, pitch-black allanite, intergrown with 

 some quartz, and weighing nearly 3 pounds, contains a number of at- 

 tached perfect crystals of allanite up to 15 mm. long by 5 mm. broad. 

 Much of the surface of the massive specimen is highly oxidized and is 

 encrusted with an appreciable thickness of the reddish-brown decomposi- 

 tion product. 



The associated minerals are kaolin, derived from the decomposition of 

 feldspar; dark-colored mica, more or less altered; quartz, dark yellow- 

 green epidote, and some magnetite which exhibits good cleavage and in 



'3 J. A. Cabell : Chem. News, vol. xxx, 1874, p. 141. 



'* E. P. Valentine : Loc. cit, p. 178. 



'^C. G. Memminger: Am. Chem. Jour., vol. 7, 1885-1886, p. 177. 



"^6 The writei- visited the locality in companj^ with S. D. Gooch during the summer of 

 1916, and unusually good specimens of the fresh and weathered allanite were secured 

 and analyzed by Mr. Gooch in the chemical laboratory of the University of Virginia, 

 with the results shown in the table on page 491. 



