LARSEN AND HUNTER: MELILITE 479 



line in about equal amounts with a little pyroxene, apatite, 

 perofskite, biotite, magnetite, etc. Grains of garnet several centi- 

 meters across are not uncommon. 



BLUE ANATASE 



Beautiful, dark blue crystals of anatase were found in narrow 

 veinlets and in the adjoining altered country rock about half a 

 mile north of the Lot Mine. The veinlets are only a few milli- 

 meters across although the rock on either side is altered for 

 several millimeters. These veinlets were found only in a single 

 dike of a dioritic rock a few hundred feet across, but in this 

 dike were observed in abundance for a distance of nearly a mile 

 and doubtless continued beyond the limits of observation. They 

 are commonly nearly parallel to the walls of the dike, but some 

 trend across the dike, thus forming a network; they probably 

 filled shrinkage joints in the diorite. 



The anatase originally formed somew^hat less than half the 

 vein filling; the other minerals of the filling are altered to limonite 

 and no trace of their original character was found. In addition 

 to occurring in the vein anatase is present in disseminated crys- 

 tals in the adjoining altered country rock.*' 



The anatase crystals are commonly well formed and are bound- 

 ed by a large number of faces. Their habit is pyramidal, tabu- 

 lar, or prismatic. In size they reach a centimeter in greatest 

 dimension. In color the mineral varies from deep blue to almost 

 black. The lighter colored crystals are translucent and some, 

 if of sufficient size, might make beautiful gem stones with their 

 deep blue color and highly adamantine luster. An approximate 

 chemical analysis showed that the blue mineral is essentially 

 TiOo. Optically it is uniaxial, negative, has a strong birefring- 

 ence and an index of refraction (w) of about 2.56. 



^ Specimens shown us by Mr. Frank L. Hess, of the Geological Survey, from 

 near Hot Springs, Arkansas, show anatase and pyrite in veinlets and the accom- 

 panying altered countrj^ rock and somewhat resemble the material described in 

 this paper. 



