Oct. 4, 1921 watson: lazulite 387 



phyllite, hematite, quartz, and muscovite. In addition to these, 

 Shepard" reported barite, minute perfectly formed transparent crystals 

 of sulfur, crystals of pyrite, and traces of gold. The locality is 

 probably best known for the occurrence of rutile, crystals of which 

 have been figured and described by European crystallographers. 



The ridge locally known as Graves Mountain has a length of 2 

 miles along an approximate northeast-southwest direction, is less 

 than half a mile wide, and rises several hundred feet above the surface 

 of the surrounding Piedmont Plain. The slopes of the ridge are very 

 unequal, and are greatly roughened from weathering. 



Graves Mountain is composed of Cambrian quartzite of which 

 there are two facies:^ (1) a foliated quartzite schist which forms 

 the basal portion of the ridge and extends some distance up the slope 

 on the northwest side, and (2) a fine-grained massive quartzite (ita- 

 columite), which forms the crest and upper slopes. Both are com- 

 posed dominantly of quartz with the difference in chemical compo- 

 sition shown in the following partial analyses: 



Quartzite Massive quartzite 



schist (itacolumite) 



SiOa 79.18 69.74 



AI2O3 14.14 24.86 



FeaOs 3.17 0.53 



Igneous rocks are not known to occur in the ridge proper, but are 

 common in the surrounding area. 



Lazulite, a rare basic phosphate of aluminum, magnesium, and 

 ferrous iron, corresponds to the formula (Fe, Mg) (A10H)2(P04)2 in 

 which the ratio of Fe: Mg(Ca) varies^ from 1:12 to 2:3. It and the 

 associated minerals occur in the itacolumite of the crest and higher 

 slopes of Graves Mountain. The lazulite is irregularly distributed 

 through the itacolumite in rude nests or bunches of single crystals 

 and crystal aggregates. Quartz veins of a few inches thickness cut 

 the quartzite on top of the ridge and sometimes carry rutile, pyro- 

 phyllite, and iron oxide, but lazulite has not been observed in them. 

 The lazulite is imbedded in the itacolumite usually as crystals which 

 range in size up to an inch in length, but as a rule the individual 

 crystals are much smaller. It also occurs massive without distinct 

 crystal boundaries. The crystals are usually acute pyramidal in 



2 C. U. Shepard. Amer. Journ. Sci. 27: 36-39. 1859. 



^ For a detailed description, including petrography, of the two facies of the quartzite, 

 see Thomas L. Watson and J. Wii,Bxni Watson, A contribution to the geology and mineralogy 

 of Graves Mountain, Georgia. Univ. of Virginia Publications, Bull. Philos. Soc, Sci. Sec, 

 1: 220-221 (No. 7). 1912. 



* E. S. Dana. A system of mineralogy, pp. 798-799. 



