138 Experiments and Obfervations 



gray, fometimes inclining very much to brown; and they 

 are completely opaque. They may, with great eafe, be 

 broken in all directions : their fracture is conchoid, and 

 fhows a fine, fmooth, compact grain, having a fmall degree 

 of luftre, refembling in fome meafure that of enamel. Their 

 hardnefs is fuch, that, being rubbed upon glafs, they act upon 

 it in a flight degree; this action is fufficient to take oft' its 

 polifh, but not to cut it : they give faint fparks when ftruck 

 with ft eel. 



Another of thefe fubftances, is a martial pyrites, of an in- 

 determinate form ; its colour is a reddifh yellow, flightly in- 

 clining to the colour of nickel, or to that of artificial pyrites. 

 The texture of this fubftance is granulated, and not very 

 ftrongly connected : when powdered, it is of a black colour. 

 This pyrites is not attractable by the magnet; and is irregu- 

 larlv diftributed through the fubftance of the ftone. 



The third of thefe fubftances confifts in fmall particles of 

 iron in a perfectly metallic ftate, fo that they may eafily be 

 flattened or extended by means of a hammer. Thefe par- 

 ticles give to the whole mafs of the ftone the property of 

 being attractable by the magnet ; they are, however, in lefs 

 proportion than thofe of pyrites juft mentioned. When a 

 piece of the ftone was powdered, and the particles of iron 

 feparated from it, as accurately as poffible, by means of a 

 magnet, they appeared to compofe about T | - 6 th of the whole 

 weight of the ftone. 



The three fubftances juft defcribed are united together by 

 means of a fourth, which is nearly of an earthy confidence. 

 For this reafon, it is eafy to feparate, with the point of a 

 knife, or even with the nail, the little globular bodies above 

 mentioned, or any other of the conftituent parts of the ftone 

 we may wifh to obtain. Indeed the ftone itfelf may readily 

 be broken merely by the action of the fingers. The colour 

 of this fourth fubftance, which ferves as a kind of cement 

 to unite the others, is a whitifh gray. 



The black cruft with which the furface of the ftone is 

 coated, although it is of no great thicknefs, emits bright 

 fparks, when ftiuck with fteel : it may be broken by a ftroke 

 with a hammer, and feems to pofTefs the fame properties as 

 the very attractable black oxide of iron. This cruft is, how- 

 ever, like the fubftance of the ftone, here and there mixed 

 with fmall particles of iron in the metallic ftate : they may 

 eafily be made vifible by pafling a file over the cruft, as they 

 then become evident on account of their metallic luftre. This 

 is more particularly the cafe with refpect to the cruft of thofe 

 flones which remain to be mentioned, they being much 



more 



