THE LEOPARDITE OF NORTH CAROLINA 



223 



monizes closely with the microscopic study of thin sections of the rock, 

 for the absence of ferromagnesian minerals accounts for the very 

 slight amount of MgO present, while the practical absence of CaO 

 and the large percentage of NagO prove the plagioclase to be albite, 

 as indicated above by the microscope. 



This analysis is compared in the table with a recent, more detailed 

 one (II), of a quartz porphyry occurring in the northwestern part of 

 the state, and with a spherulitic rhyolite (III) found east of the 

 Charlotte locality in Montgomery county; and with analyses IV and 

 V of well-knoAvn quartz porphyries occurring in other parts of the 

 United States. A perusal of the figures given in the table will make 

 clear the general similarity of the rocks, notwithstanding the rather 

 striking differences indicated in some of the constituents. 



TABLE OF ANALYSES. 



II 



III 



IV 



V 



SiOg 



A1203 



Fe,03 



FeO 



MgO 



CaO 



Na^O 



K2O 



H..O-iio°C. 

 HoO+iio°C 



TiOs 



P2O5 



ZrOo 



MnO 



SrO 



BaO 



LigO 



NiO 



CO3 



Total . . . 



79-75 

 10.47 

 0.64 

 0.92 

 0.13 

 0.15 

 1.36 

 6.01 

 0.08 

 o. 60 

 0.15 

 trace 

 0.05 

 trace 

 trace 

 0.06 

 trace 



79-57 

 II .41 

 0.20 

 o. 70 

 a little 

 0.21 

 346 

 3-52 

 0.18 

 0.61 



O. II 



trace 



0.05 



73.12 

 14.27 

 0.51 

 0.26 

 0.24 

 1 . 10 



3-43 

 4.90 

 0.68 



0-73 

 0.08 

 0.03 



0.06 

 trace 

 trace 

 trace 



0.77 



72.8s 



13-78 

 1.87 

 0.36 

 0.42 

 0.87 

 4.14 

 4.49 

 0.22 



0-54 

 0.44 

 0.13 



0.06 



100.37 



99.87 



I. Quartz porphyry (leopardite), one and a half miles east of Charlotte, Meck- 

 lenburg county, North Carolina. American Journal of Science, Vol. XXXIII 

 (1862, 2d ser.), p. 198. F. A. Genth, analyst. 

 II. Quartz porphyry — two and a half miles northwest of Blowing Rock, Watauga 

 county, North Carolina. Petrographic data by Arthur Keith. Contains 

 quartz and orthoclase, with subordinate sericite, chlorite, and biotite. W. 

 F. Hillebrand, analyst. Bulletin No. 168, U. S. Geological Survey, p. 52. 



