296 CHEMICAL JNALTSIS of an 



inftances to be fo\ir-(icled and redlangular. Their length is from 

 half an inch to two inches ; but their thicknefs does not exceed 

 one-fortieth or one-fiftieth part of an inch. None of thefe fi- 

 bres can be broken aci'ofs, fo as to prefent an even furface ; for 

 they break irregularly, and become divided at the point of frac- 

 ture into very minute fpiculse, which alfo affume a fomewhat 

 re(5tangular fhape. 



The fmall (piculae or fibres are tranfparent and colourlefs, 

 ■with a confiderable degree of luitre ; but the unbroken part of 

 the Hone polTefles lefs luftre than the feparate fpiculse, and much 

 lefs tranfparency, from a want of compadlnefs, and from the 

 effect of many minute cracks. 



Its hardnefs is not eafily determined, on account of brittlenefs ; 

 but when a piece of it is rubbed againft glafs, though the fibres 

 crumble down very quickly, yet the glafs is flightly fcratched at 

 the fame time. Small fragments of it can be broken with the fin- 

 gers, or crudied by preilure, into very flender fpiculs, which 

 are iliarp, and apt to penetrate the hands when touched. Al- 

 though the cohefion of its component parts be fo weak, yet it 

 bends, and yields in fome meafure before it breaks, and is not 

 eafily ground to powder in a mortar. 



I FOUND the fpecific gravity of different pieces of the fpecl- 

 men, taken in diftilled water at the temperature of 60°, to vary 

 from 2.643 '^^ 2.740. 



This flone has the property of appearing luminous in a dark 

 place, both by friclion and by heat. A very flight degree of 

 fridion produces this effedl ; for a perfon can eafily diflinguifh 

 a phofphoric light, even if he draws his finger acrofs it. "When 

 ftruck with a hammer in fuch a manner that fmall fragments 

 ar • driven off, they appear luminous in pafling through the air,, 

 and continue tolhine for a moment after falling on the ground; 



and 



