418 Pirsson — Petrography of Tripyramid Mountain. 



busch* likens to the structure of meteorites. The specks of 

 metallic iron mentioned by Haw est I was not able to find, but 

 some pyrite was observed. 



The biotite is of a deep red brown and very pleochroic ; 

 while it occurs in isolated flakes it is usually seen as a mantle 

 coatino- the ore grains. 



Apatite is not common, but is seen occasionally, often in 

 slender prisms in feldspar. 



Mode. — The actual mineral composition, determined by 

 observation of the sections and calculation from the chemical 

 analysis, is shown in the adjoining columns : 



Texture. The texture is that 

 of a typical gabbro, a granular 



Labradorite 63-0 one, conditioned by the short, 



Biotite 5-0 broad laths of feldspar, with the 



Pyroxene 14-0 intermingled shapeless masses of 



Olivine 100 pyroxene, olivine and ores. Thei-e 



Iron ore 6-7 is no tendency to the ophitic tex- 



Apatite 1*3 ture by the enclosure of feldspar 



laths by pyroxene, indeed the only 



Total 100-0 case of this kind noted was where 



the feldspar in one or two cases 

 was enclosed by iron ore as previ- 

 ously stated. 



Chemical Composition. — For a chemical analysis of this 



rock, I am indebted to Mr. C. J. Monahan, whose results are 

 given in No. I of the following table : 



No. I. II. III. IV. V. VI. VII. 



Si0 2 ... 47-82 47-88 53'18 52"8 53-65 48.67 0-797 



A1 S 3 .. 19-99 18-90 23"25 17'8 20-77 16-88 0-196 



Fe 2 3 .. 2-10 1-39 1'53 1'2 0-98 4"98 0'013 



FeO ... 6-48 10-45 1-82 4-8 7"61 6-37 0-090 



MgO... 4-94 7-10 260 4-8 1'57 4-62 0-123 



CaO 11-65 8-36 11-18 12-9 9-16 8-63 0-208 



Na 2 .. 3-51 2-75 3"97 3-0 3-33 3-85 0-056 



K 2 0-67 0-81 0-86 0-5 T61 1'26 0"007 



H a O+ . 0-21 0-43 0-98 12 1-33 0"32 



H 2 0— . 0-07 0-18 0-15 0-02 



CO, none 012 0*34 - 



Ti0 2 ... 2-00 1-20 0-45 0"5 ? 2-12 0-025 



P 2 6 ... 0-56 0-20 0-09 ? ? 185 0004 



S 0-07 



Cr 2 O s tr. 



NiO 0-02 -- 



MnO... tr. 0-16 0-11 tr 



BaO tr. tr. tr tr 



100-00 10002 100-51 99-5 100-01 99-57 

 Mass. Gesteine, 4 te Aufl., p. 336. f Loc. cit., p. 167. 



