UNCOMMON SPECIES of ZEOLITE. 297 



and a hard body drawn over it leaves a track of light, which 

 remains a fecond or two vifible. When a piece of the ftone is 

 pounded quickly in a mortar, a ftrong light is emitted ; but 

 after being wholly reduced to powder, it no longer fliines. 



The light which it gives by flight fridtion, is fully equal to 

 that produced by two quartz pebbles, rubbed or (truck againft 

 each other ftrongly. ' ^ 



Small fragments of this zeolite placed on a piece of hot iron, 

 or of clay, alfo become luminous, and fhine with nearly as 

 much brightnefs as common blue fluor does, when heated in 

 the fame manner. By being made red-hot, however, it is de- 

 prived of the property of giving light afterwards by heat, 

 though it ftill appears faintly luminous by fridlion. In all 

 thefe experiments it is a reddifh white light which it emits, ac- 

 companied at times with reddifh momentary kind of flaflies. 



It can be melted without difEculty into glafs. ■ When a fmall 

 piece of it is heated gradually with the blowpipe, it firfl be- 

 comes white and opaque ; a number of fifTures are then form- 

 ed, by which its bulk appears fomewhat increafed ; and after 

 the flame is made fufficiently intenfe, it melts into a globule 

 of colourlefs glafs, the tranfparency of which is imperfedl on ac- 

 count of many minute aii'-bubbles. Although thus fulible by 

 flrong heat, yet a very low degree of ignition fcarcely afFeds it. 

 A piece of the flone, after having been put into a crucible, and 

 expofed for a fhort time to a fire which madeit juft vifibly red- 

 hot, was not altered in appearance, and had not lofl more than 

 fio part of its weight. In a temperature, however, about 20° 

 of Wedgwood, I found that a fragment of this zeolite became 

 opake, and more eafy to pulverize than in its natural ftate ; at 

 go*' it did not melt, but was glazed on the furface, adhered to 

 the crucible, and had begun to fink down; and at 120° melt- 

 ed into an imperfecl glafs of a light greenifli yellow colour, 



deficient 



