1915] The Ottawa Naturalist. 65 



Phlogopite. 



The colour of this mineral varies from amber brown to a 

 almost white. The largest crystals are about four inches 

 across but are too imperfect to be of economic value. 



DiopsiDE, Macdonald Island. 



Crystals of diopside sometimes three inches in length occur 

 in calcite. They are olive green in colour with very fresh, 

 brilliant surfaces in the prism zone while the terminal faces 

 are often rounded and even corroded. The habit of the 

 crystals is peculiar in that the most prominent end face is 

 the positive orthodome (101). Basal cleavage or parting 

 is so well developed that most of the crystals have been 

 broken across showing very smooth cleavage surfaces. The 

 material is much brighter and fresher than the diopside 

 found to the north of the city of Ottawa. Owing to the 

 unusual crystal habit and the degree of corrosion this 

 mineral merits further study. 



Spinel, Locality unknown. 



The mineral occurs in the form of octahedra whose edges 

 are sometimes trtincated by the rhombic dedecahedron. 

 The largest crystals are about half an inch in diameter. 

 The crj^stals are lilac in colour but too much fractured to be 

 of value for gem purposes. 



CoRDiERiTE, Garnet Island (Long 72° 30', Lat. 63^ 45'). 



The specimens of cordierite consist of irregiilar fragments 

 of vitreous lustre which are sometimes two inches in dia- 

 meter. It is associated with white felspar rock and prob- 

 ably occurs as lenses in gneiss. The mineral is deep blue 

 in colour and some of the fragments are sufficiently free 

 from flaws to stiggest its use as a gem mineral. Cordierite 

 has up to the present been a very rare mineral in Canada so 

 that its discovery in Baffin Land has considerable minera- 

 logical interest. 



In thin sections under the microscope the mineral is seen 

 to be polysynthetically twinned so that it is difficult to 

 believe that the section is not composed of plagioclase. A 

 subordinate part of the cordierite consists of an intimate 

 intergrowth of twinned mineral in which the two portions 

 present a vermicular intergrowth.* It is also characteristic 

 that though the cordierite as seen in thin sections there are 

 distributed many small inclusions of rutile or zircon, each of 

 which is surrounded by a deep pleochroic aureole, orange 

 in colour. 



* Walker and Collins., Rec. Geol. Survey of India, Vol. XXXVI., p. 1. 



