MINERALS AND GEOLOGY 







Dr. Sterry Hunt. It consists of two crystals of diopside, like Fig. 

 65, united by a front vertical face, and much extended or flattened in 

 this direction. Pyroxene occurs also very commonly in acicular and 

 fibrous groups, and in cleavable and also granular masses. Cleavage 

 planes meet at angles of 87 5' and 92 55'. H (except in altered or 

 abnormal varieties) = 5.5 6.0 ; sp. gr. = 3.2 3.5. BB, melts 

 in. general without difficulty, the dark varieties yielding in most 

 cases a magnetic bead. Scarcely or not at all attacked by acids. In 

 composition, essentially a bisilicate of magnesia and lime, with part 

 of these bases replaced by protoxide of iron, &c. A small amount of 

 alumina is likewise occasionally present, as in Amphibole, the com- 

 position of these two minerals being practically identical. Pyroxene 

 and Amphibole are also closely allied by crystallization and physical 

 characters, but their crystals have a more or less distinct aspect, and 

 the cleavage angles are not alike. Pyroxene exhibits also, as a general 

 rule, a somewhat higher density, its sp. gr. varying usually from 3.25 

 to 3.35, whilst that of Amphibole lies most commonly between 2.9 

 and 3.2. Light-coloured varieties of pyroxene are usually known as 

 Diopside (also as Sahlite, Malacolite, Traverselite, Alalite, <fec.), 

 whilst the term Augite is generally applied to the dark varieties. 

 (Jeftersonite, Hudsonite, Hedenbergite, Coccolite, <kc., are other 

 synonyms of this species.) 



Pyroxene is of common occurrence in eruptive and metamorphic 

 rocks (see Part III). It is especially characteristic of modern vol- 

 canic products, but occurs also in many of the more ancient trappean 

 formations. In Central Canada, it is found in white and pale-green 

 crystals in many of the Laurentian crystalline limestones, as at Calu- 

 met Falls and elsewhere in the Ottawa district. Also in large 

 crystals, with amphibole, at the High Falls of the Madawaska ; with 

 mica, apatite, &c., in Bathurst ; in well-defined crystals with pyrites 

 in a quartz vein near Belmont Lake ; in the anorthosites or Upper 

 Laurentian strata of Chateau Richer ; and elsewhere in these older 

 metamorphic strata. In the higher series south of the St. Lawrence, 

 it occurs with garnets, <fec., in Orford Township. Finally, well-defined 

 black crystals are imbedded in the trap of the Montreal Mountain, 

 and also in the erupted traps or dolerites of Rougemont and Montar- 

 ville. Acmite, a related silicate in thin, black crystals, occurs 

 according to Dr. B. J. Harrington, in the nepheline syenites of 

 Montreal and Beloil. 



