290 Count de Bourdon’s Description of 
having rubbed them together, the latter seemed to be the most 
worn of the two. It gives bright sparks, upon being struck with 
steel. Collision causes it to emit a phosphorescent light, of a 
deep reddish colour. It cannot, by friction, be made to give 
signs of electricity. 
Its mean specific gravity, taken from four trials, is 3214. 
This substance was tried with a blowpipe, by Mr. Fleuriau 
de Bellevue, a mineralogist much accustomed to such opera- 
tions, and found to be absolutely infusible, even when placed, 
in very minute particles, upon cyanite. 
The external texture of this substance is usually fibrous ; the 
fibres being very fine, and closely connected together. When 
it is broken according to the direction of the fibres, its internal 
texture appears to be exactly the same ; but, if it is broken in a 
direction transverse to the fibres, its texture appears to be com- 
pact. The lustre of the last kind of fracture is rather vitre- 
ous ; and there is nothing in its appearance that gives reason 
to think it was made in the direction 01 the laminae. When we 
wish to try the hardness of this stone, it should be done in a 
direction which is transverse or perpendicular to the fibres ; not 
in a direction parallel to them. 
There exist many pieces of this substance that are merely 
irregular aggregations, in which the fibres cross each other, in 
bundles, in different directions. I have only once seen it in a 
form which could be considered as a determined one ; viz. a 
rhomboidal tetraedral prism, of about 8o° and 100, the ter- 
minal faces of which are imperfect. But, as this prism, although 
pretty regular in its form, is the only one I have }^et been able 
to discover, the above observation requires to be repeated, 
before we can safely make any dependence upon it. I must 
