2g6 CHEMICAL ANALTSIS of an 



inftances to be four-fided and rectangular. 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 acrofs, fo as to prefent an even furface ; for 

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

 ture into very minute fpiculae, which alfo afTume a fomewhat 

 rectangular fhape. 



The fmall fpiculae or fibres are tranfparent and colourlefs, 

 with a confiderable degree of luftre j but the unbroken part of 

 the f tone poffeffes lefs luftre than the feparate fpiculae, and much 

 lefs tranfparency, from a want of compactnefs, 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 crufhed by preffure, into very flender fpiculae, which 

 are iharp, 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 fpeci- 

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

 from 2.643 to 2 -74°« 



This flone has the property of appearing luminous in a dark 

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

 friction produces this effect: ; for a perfon can eafily diftinguifh 

 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 pa/ling through the air, 

 .and continue tofhine for a moment after falling on the ground; 



and 



