﻿part 3] VOLCANIC ROCKS OF MOZAMBIQUE, 235 



Several analyses of solvsbergite from other localities are tabu- 

 lated below for comparison with the Mozambique example. All 

 the analyses bear a close family resemblance, indicated in the 

 quantitative classification by their falling into divisions 1,5,1,4. 

 or II, 5, 1, 4. The Mozambique solvsbergite is richer in iron-oxides, 

 both ferric and ferrous, than any other hitherto analysed. The 

 abundance of ferrous iron, which is the more noteworthy, is clearly 

 related to the dominance of cossyrite over the more usual segirine, 

 and in part to the presence of magnetite : — 





A. 



B. 



C. 



D. 



E. 



F. 



SiO., 



61-02 



63-74 



65-46 



64-28 



64-92 



58-90 



A1 2 0 3 



17-11 



17-86 



17-40 



15-97 



16-30 



17-70 



Fe.,0 3 



4-37 



4-27 



3-00 



2-91 



3-62 



3-94 



FeO 



3-42 



0-30 



1-60 



3-18 



0-84 



2-37 



MgO 



0-63 



0-10 



0-09 



0-03 



0-22 



0-54 



CaO 



1-20 



0-83 



0-76 



0-85 



1-20 



1-05 



Na.,0 



6-51 



7-23 



6-51 



7-28 



6-62 



7-39 



K 2 0 



4-47 



5-19 



4-74 



5-07 



4-98 



5-59 



H 2 0 



0-64 



0-83 



0-87 



0-20 



0-50 



1-90 



Tib, 



0-59 



tr. 



0-24 



0-50 





0-40 



P 2 O s 



n. d. 







0-08 







MnO 



0-34 



0-19 





. tr. 



0-40 



0-55 



Totals 



100-30 



100-54 



100-67 



100-35 



99-60 



100-33 



A. Between Miali and the Sanhuti Biver, Mozambique (an. Holmes). 



B. Edda Grijorgis, Abyssinia (an. Prior). 



C. Camel's Hump, Victoria, Australia (an. Bailey, Lewis, & Hall). 



D. Andrews Point, Essex County, Mass., U.S.A. (an. Washington). 



E. Solvsberget, Gran, Norway (an. Schmelck). 



F. Kjose, Aklungen, Norway (an. Schmelck). 



IX. ^gieike-Teachyte. (PI. XX, fig. 2.) 



Fragments of a porous lava with small phenocrysts of felspar 

 (anorthoclase) and strongly developed flow-structure were found 

 north of Sokoto Hill (151 & 152). Mr. Starey and I worked 

 in the district for several weeks, but failed to discover the rock 

 in situ. The weathered surface of the specimens collected -has 

 a rusty-red colour, broken by white-lined vesicles, the contents 

 of which prove to be opal (refractive index between 1*446 = 

 chloroform, and P472 = nut-oil). Within, the rock presents a 

 mottled appearance, similar to, but more finely granular than, that 

 of the solvsbergite just described. Specific gravity = 2-33. 



Under the microscope the minerals that can be distinguished 

 are anorthoclase, segirine, cossyrite, magnetite, and opal. In 

 addition, a great deal of an obscure brown alteration-product is 

 present ; similar material in the trachytes of the Great Rift Valley 

 has been called ' ferrite ' by Dr. Gr. T. Prior. As in the Pift- 

 Valley rocks, so here, the 'ferrite ' seems to be an alteration -product 

 of cossyrite and other soda-amphiboles, for its mode of occurrence 



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