On the jirfenlates of Copper and of Iron. T4I 



thcfe cryftals, I have not vet been able to determine the 

 niearure of their ansrles. The prifm is terminated at each of 

 its extremities by aletraedral pyramid, which is pretty ftiarp; 

 and its planes, which are fcalene triangles, unite by pairs, 

 forming elonoated ridges, which join the acute edges of the 

 prifm r^in the other dn-eftion, they unite, alfo by pairs, fo as 

 to form a ridae which is lefs elongated, and joins the obtufe 

 til^efi. Very often the obtufe edges of the prifin are replaced 

 bv^planes {of greater or lefs extent) equally inclined upon 

 the adjacent ones. (Fig. 31.) Sometimes the acute edges 

 are alio replaced in the fame manner, but always by planes 

 of lefs extent. (Fig. 33.) 



The above are" the only varieties I have obferved of this 

 arfeniate. Its cryftals fcld'om occur fingly, being generally 

 grouped together, in a very irregular manner ; fometimes, 

 however, they are fo united as to affume a mamillated form, 

 having the pyramids of the cryftals which compofe the ma- 

 millae all placed upon the furface thereof. 



The fpecific gravity of this arfeniate is 3,400. 



Its hardnefs Ts rather greater than that of the fimple arfe- 

 niate of iron : it fcratches calcareous fpar with greater faci- 

 lity, but does not fcratch fluor fpar, on heavy fpar. 



Its colour is that of a very faint (ky-blue ; fometimes the 

 blue colour is a little deeper. I have feen fome cryftals which 

 had the fame brown relin colour as the preceding fpeciesj 

 but they are very rare. 



Hitherto I have never met with this fpecies in any other 

 form than that of a perfeft cryftal. 



■ XXV^I. Anahfts of the Arfcniatcs of Copper and of Iron, 

 ^ ' By Richard Chenevix, Efq. >. R. S. M. R.^I.A* 



SECTION I. 



f~^-y Arfeniatcs of Copper, 



X HE endlefs divcrfity which the hand of Nature has dif- 

 fufcd through all her works, even when (lie makes ufe of the 

 fame primitive materials, muft fufficienlly convince us, that, 

 whatever accuracy we may attain in the knowledge oi the 

 latter, the mi-HUs which Hie cmplovs to form her combina- 

 tions are (till icciet. The intelleAual eye may indulge in the 

 contcinplaiion of hvpotlietic fyftenis, which iti'elf has cre- 

 ated, and wliich it alone can behold; but how far removed 



* /rota Jiu'-'i'tUiii/n.' vf the Ro^al Socieij of London for 1801. 



muft 



