4'!^ On a nezu Viirletyof.Epidotet 



Vhyjkal Chtita6lefi. 



■ Specific gravity 3 "3 739. This charafter was proved on the 

 purefl iragnicnts that could be pictciircd. 



Hardnefs. It eafily fcratchcs glafs; it is with difficulty 

 fcralcbed bv (juarlz ; (Irikes flie with ftee!. 



Tyanfpare-ifcy,-, Pellucid on the edges. 



Qolour. Bright gray. 



i^le&ncily. I^one by heat ; acquires none by long con- 

 tinued friction. 



Geometric CbarttSlers. 



Pri7>iitivc /p.rvi. A ri2;ht prifm with rhombal bales 5 

 inclination of the planes hi a;id T of the prifin (fig. 3, 

 Pkuelll.) 114" 37' and 6_5' 23'. The dlvifions parallel 'to 

 th< planes are generally very clofc; the laminae are feldoiii 

 obferved in the' direction of the bafcs. . .'";;i ■ .. 



Structure. Very fenfihly lamellar: the riatiiral joinings 

 feem to be fomewhat clofer in one direction than in another. 



FraSlure. Conchoid^ (Lining, with fmall cavities: it 

 takes place only in one di'-eAion, that of the bafes; in that 

 of the planes of the prifni nothing is obtained but laminae, 

 which manifell the ftru6ture. 



Chemical Characters. 



With the blow-pipe. On the firfl application of heat the 

 colour becomes lefs dark ; the angles and the ridges then fufe 

 into a yellowiih enamel, which grows brown in a continued 

 heat, and is converted into fcoria : if a thin plate l^e fub- 

 jectcd to experiment, , it becomes corneous before it is fco- 

 rified. 



Acids, cold. Acids have no afilion on it. 



It rcfults from this examination, and particularly the con- 

 fidcration of the eflcnti&l character, that the fubftancc in 

 queflion bclontrs to the epidote : for it can be divided in a 

 direftion parallel to the planes of a right rhomboidal prifm, 

 which form with each other angles of 114° 37' and 6^^ 23'. 

 It fomctimcs happens that there is obferved above the planes 

 of the priftn facets oblique to the axes, which might give 

 realon to fuppofe that they are parallel to the bafes, and 

 thence be led into an error refpe6ting the determination of 

 the, primitive form; but an attentive examination fhows that 

 thev bi-'long to other crydals which penetrate the former; 

 and befides, the examination of a form, fufiicienlly prorai- 

 lant to admit of applying to it the laws of (Irutfture, has 

 proved that obfervation agrees with calculation. 

 * This 



