HYDRON SILICATES IN ROCKS OF CONCEPTION BAY 137 



prospected to depths of 15 and 20 feet, probably under the 

 misapprehension that they carried pyrophyllite. A chemical 

 analysis of the pinitized groundmass of the spherulitic rhyolite is 

 given on p. 137 (No. 8). 



CHEMICAL ANALYSES 



Chemical analyses of eight typical rocks showing the various 

 types and some of the stages of the alterations and replacements 

 which have affected the volcanics are here given. These analyses 

 were recalculated to correspond approximately to the mineral 

 composition of the rocks. Small amounts of water of absorption, 

 iron oxides except in No. 7, excess alumina, etc., have been lumped 

 together as such under "other constituents." This involves of 

 course a slight but inappreciable error in the proportions of the 

 other minerals. It is probable that some sericite is also present 

 in rocks Nos. 3 and 4, but owing to the difficulty of distinguishing 

 sericite from pyrophyllite under the microscope, and because 

 of the fact that the decrease in potash with an increase in water 



TABLE I 

 Showing Character of Alterations of Rhyolite 



Si0 2 . . 

 A1 2 3 . 



Fe 2 3 - 



FeO.. 

 MgO. 

 CaO. . 

 Na 2 0. 

 K 2 0.. 

 H 2 0+ 

 H 2 0- 

 MnO. 



Sp. G. 



76.24 



13-94 



0.89 

 0.13 

 0.27 

 1.07 

 2-55 

 4-95 

 0.15 

 0.03 

 Trace 



80.60 



11.27 



0.89 



0.08 



0.31 

 0.66 

 1. 16 

 4.68 

 0.49 

 o. 11 

 Trace 



74-Si 



17.12 

 1.28 



. 0.08 

 0.04 

 0.13 

 0.48 

 3-68 

 2.44 

 0.09 



Trace 



72. 10 

 21.51 



o.54 



n.d. 



0.04 



0.49 



0.42 



2. 21 



3 09 

 0.23 

 n.d. 



65.04 

 29.49 

 0.28 

 n.d. 

 0.04 

 o. 10 

 o-33 

 °-33 

 4.84 

 0.03 

 n.d. 



88.09 



9-53 



o. 20 



n.d. 



0.05 



0.58 



n.d. 



n.d. 



1.68 



0.04 



n.d. 



54-47 

 27.14 

 2.58 

 o.47 

 2.44 

 0.81 

 0.68 

 8.01 



3-44 

 o. 27 

 0.09 



100. 22 

 2.64 



100.25 

 2.64 



99 -8S 

 2-73 



100.63 



2.77 



100.48 

 2.83 



100.17 100.40 

 2.70 2.82 



61 .07 

 22.99 

 1.56 

 0.42 

 0.65 

 1.63 

 0.63 

 7 .58 

 2-93 

 0.23 

 0.17 



99.86 



2. 70 



1. Unaltered dark-gray flow rhyolite (228 D 1 c). 



2. Silicified drab spherulitic rhyolite (228 F 2). 



3- Pyrophyllitized rhyolite. Matrix of lenses; talc prospect 2 (228 F 3). 



4- Pyrophyllitized rhyolite. Matrix of spherulite; talc prospect 1 (222 E 2 j). 



5- Pyrophyllite. Light greenish-yellow waxy pyrophyllite from talc prospect 1 (222 E : 

 6. Quartz-pyrophyllite schist. Nodule in pyrophyllite (5); talc prospect 1 (222 E 2 g). 

 7- Pinite; dark dirty -green waxy, matrix of spherulitic rhyolite. Manuels (228 D 1 h). 

 8. Pinite schist. Matrix of spherulitic rhyolite, Harbour Main (232 E 2 b). 



f). 



