BY W. A. MACLEOD AND O. E. WHITE. 



75 



Comparing the analysis of the mineral with the published 

 analysis of the different species of garnet, it will be seen 

 that this is a new variety. In no other recorded types do 

 the oxides of Mn., Mg., and Ca. bear the same proportion 

 to each other, with the exception of some Iron Alumnia 

 Garnets, and there the percentage is much lower, being 

 only between 3°/^ and 4:°/o of each base. 



The Specific gravity = 



Hardness = 7*5. Fusibility = 3'5 about. 



I. Analysis of massive Garnet from Brazil. 

 Ti. ,, „ Garnet, Port Cygnet. 

 III. „ „ Trachyte ♦„ 



Macroscopical characteristics of Garnet Trachyte. 

 Bluish-grey in colour on a fresh fractured surface, studded 

 with crystals of garnet. 



Microsaypical characters. — The holocrystalline ground- 

 mass is made up of lath-shaped sanidine felspars, the 

 interspaces being filled with brown mica. No Plagioclase 

 seems to be present, or if so, is difficult to distinguish from 

 the sanidine. Carlsbad twins, as well as single individuals, 

 are plentiful. Fluxional arrangement of the felspars is 

 evident. 



Sanidine also is present as phenocrysts, having both 

 tabular and columnar habit, and in some cases shows a 

 zonal tendency. Decomposition of some of the crystals 

 has set in with alteration to muscovite.(?) 



The ferro magnesian mineral is a brown Biotite without 

 idiomorphic character. It is strongly pleochroic. Mag- 

 netite is sparingly scattered through the ground-mass, and 

 appears to have resulted from the decomposition of the 

 mica, generally accompanying the latter. 



