438 THE CANADIAN NATURALIST. [Vol. ix, 



pitting or indentation, which almost reqnires a microscope for 

 observation. They are without striation. The color is black, 

 with a slight intermixture of gray and blue. In a few instances 

 an area of cyanite-blue occupies a face of the larger crystals^ 

 but only to a slight depth from the surface. This part of the 

 crystal is semi-transparent; while for the rest, tiie entire mineral 

 is dark ash gray to bluish black, and only translucent on the 

 edges. The vertical cleavages, parallel with the primary prism, 

 parallel with the narrower planes in the quadrangular prisms. 

 Only traces of a transverse cleavage exist. A marked peculi- 

 arity of the larger crystals is the regular interlamination of thin 

 films of white calcite, parallel with the eight sides of the prism. 

 These layers, to the number of two or three, are equi-distant, 

 thus imparting to the fractured ends of the crystals a checkered 

 aspect, sti ongly suggesting the structure of chiastoiite.^ Luster, 

 resinous to vitreous. Hardness = 7- . . . 7-5. Specific grav- 

 ity, 2.608. 



A very striking peculiarity of the .mineral is the extremely 

 fetid odor occasioned by its fracture ; nor does this cease to be 

 emitted uatil the fragments are reduced to an impalpable pow- 

 der. The color of the powder is a bluish ash gray. It -cannot 

 be regarded as a hydrated mineral, as its content of water does 

 not exceed 1*6 p. c. By exposure, however, to full ignition in 

 a shallow platinum dish for several hour?, it loses 4*6 p. c, this 

 loss proceeding from the presence of organic matter, graphite, 

 and carbonic acid from the decomposition of carbonate of lime. 

 The powder still partially retains its grayish tint after long 

 ignition ; and it is only before the blowpipe that the portion 

 most strongly heated loses its color. The thinnest part then 

 undergoes fusion, attended by a feeble ebulition, into a colorless 

 transparent glass. 



Owing to the variable presence of graphite, calcite and quartz, 

 the chemical examination is attended with uncertainty. The 

 Si02 varied from 48-65 to 51-o0; the AI0O3 from 13-45 to 

 19-62; the CaO from 17-43 to 21-6, and the TiOg from 4-35 



* Prof. E. S. Dana lias kindly made a section of one of the crystals, 

 and examined it in polarized light. He finds " the black color to be 

 due to foreign matter, present in the form of minute grains that seem 

 to be metallic, making up no small part of the whole," and is of 

 opinion that " its analysis is not a guide to the real composition o f 

 the mineral." 



