Derby — Schists of the Gold and Diamond Regions. 207 



Aet. XIX. — Notes on Certain Schists of the Gold and 

 Diamond Regions of Eastern Minas Geraes, Brazil • by 

 Oeville A. Derby. 



In a recent communication in this Journal (May, 1899) brief 

 reference was made to certain schists of the region that were 

 supposed to be in some way related to the curious schistose 

 partings in the quartz veins that were more particularly dis- 

 cussed. The single type analyzed presented such an abnormal 

 composition that it appeared desirable to make analyses, kindly 

 executed by Dr. Hussak, of such material, unfortunately 

 scanty, as was at hand as seemed suitable for that purpose. 

 This material includes, in addition to the rock already analyzed 

 by Hillebrand, two of the rocks mentioned in the above cited 

 pajjer from the diamond mine of Sao Joao da Chapada. To 

 these has been added a perfectly sound schist found loose in a 

 topaz washing near Ouro Preto and presumed to represent the 

 decomposed material in which the nests of topaz occur. In 

 addition four analyses by Gorceix of schists of the Ouro Preto 

 region are a;iven from the Annaes da Escola de Minas de Ouro 

 Preto (volsT 1 and 2, 1882, 1883). 



I. IT. III. IV. V. VI. VII. VIII. 



Si0 2 38-32 37-77 47"83 3118 54"l 47 4 62"4 364 



A1 2 3 . 28'16 21-37 26'75 20'39 27-3 312 22'7 26-1 



Fe 2 3 2-24 28-36 8 51 3641 7-7 67 38 231 



FeO 402 



CaO 0-32 tr. tr. tr ... IS 



MgO. 12-04 105 2-43 0-79 8 2 13 2"1 



KoO 1-11 8-96 10-42 7"18 3-0 4-5 4-2 6"4 



Na 2 0-16 tr, 36 27 1-5 10 



Loss on ignition.. 8"01 3 89 5-33 3-83 38 5-6 34 39 



Other elements 5 69 



Total 100-07 101-40 101-27 99-78 100 3 100-1 99-3 100-3- 



I. — Greenish schist with large crystals of cyanite; Serra do 

 Gigante, north of Diamantina; loose block; analyst, Hille- 

 brand (this Journal, May, 1889). "Other elements" include 

 Ti0 2 4-93, Zr0 2 0-09, MnO 0-16, (NiCo)O 0'04, P 2 6 0-47 

 and traces of SrO, Li 2 0, S and F. 



II. — Bluish schist found loose in the diamond mine of Sao Joao 

 da Chapada but presumed to come from a schistose layer in 

 the lower quartzite (itacolumite) ; analyst, Hussak. Ti0 2 

 occurs rather abundantly but was not separately determined. 



III. —Soft greenish schist found loose in the diamond mine of Sao 

 Joao da Chapada but presumed to come from a schistose 

 layer in the upper conglomeritic quartzite ; analyst, Hussak. 

 A strong trace of P 2 3 was noted in the analysis. 



