ART. 2. 



PETROLOGY AT GOOSE CREEK SHANNON. 



Analysis, ratios, and norm of diabase pegmatite. 



19 



SiOj 



TiOj 



Al^O, 



FezOa 



FeO 



MnO 



CaO 



MgO 



K2O 



NazO 



P2O5 



Total 



Norm. 



Quartz 4. SO' 



Orthoclase __ 8. 90 



Albite 16. 77 



Anorthite .-. 26. 97 



Diopside 9. 50" 



Hypersthene. 27. 58 



Magnetite. _- .23 



Ilmenite 4. 41 



Apatite .67, 



> Salic, 57.44 per cent. 



> Femic, 42.39 per cent. 



This rock falls in class III, order 5, rang 3, subrang 3, kentallenose. 

 The greater abundance of micropegmatite is reflected in the greater 

 amount of quartz in the norm and the higher percentages of alkalies. 



Coarse phases of diabase sills have been described before from a 

 number of localities. Those of the Gowganda Lake region described 

 by Bowen^ are very similar as called to my attention by Doctor Bowen 

 himself, who, upon examination of the hand specimen of typical dia- 

 base pegmatite illustrated in plate 2, remarked that it could be dupli- 

 cated from the Gowganda Lake area. His description of the rock, 

 a gabbro, is as follows: 



In places the diabase has moderately coarse phases with augite in stout prisms 

 showing one perfect cleavage face, the diallagic parting, which determines the 

 fracturing of the rock. The cleavage face is nearly always bent, sometimes into 

 a considerable arc. This bending is a constant character of the augite in the 

 coarse phase from widely separated points. Under the microscope this phase 

 shows a nearly simultaneous crystallization of augite and plagioclase, the feldspar 

 in broad areas generally inclosing the augite. 



The feldspar is an acid labradorite Ab4,-, Augj, approximating that of the 

 outer zones of the crystals of the normal diabase. Some zonal growth was 

 shown in a few examples, the outer zone being slightly more acid. 



The pyroxene is augite throughout, with cleavage parallel to 100 and a lamellar 

 structure parallel to the base. Enstatite is absent. Both augite and plagioclase 



♦ Norman L. Bowen, Diabase and granophyre of the Gowganda Lake district, Ontario. Journ. Qeol , 

 vol. 18, pp. 660-G61, 1910. 



