40 



PHYSIOGRAPHY. 



Arragonite. 



Cleavage, parallel with the lateral faces of the primary 

 form. 



Fracture conchoidal, uneven. 



Surface generally smooth. The curvature of the sides 

 parallel to the prismatic axis very often produces acicular 

 crystals, variously aggregated. 



Lustre vitreous, inclining to resinous upon faces of frac- 

 ture. Color white, prevalent ; sometimes passing into grey, 

 yellow, mountain-green and violet blue. Streak greyish 

 white. Transparent . . . translucent. 



Brittle. Hardness = 35 . . . 4-0. Sp. gr. =2-931, (the 

 transparent crystals from Bohemia.) 



Compound varieties. 



Fig. 45. Fig. 46. Fig. 47. 



Arragon. 



Fig. 45. Formed from the composition of two individu- 

 als, like fig. 43, the angle of revolution being 90. 



Fig. 46. Formed from the composition of three individ- 

 uals of the same form, as explained in 73. Part I. 



Fig. 47. The dotted lines represent the cracks observa- 

 ble down each plane,-arising from the contact of the planes 

 forming the dihedral summits of the several individuals of 

 which fig. 46 is composed ; and hence the six lateral planes 

 of this apparently regular hexagonal prism are not flat; but 

 each presents a slightly re-entering angle. 



Globular, reniform, coralloidal shapes ; surface drusy, 

 composition columnar, the individuals being often very del- 

 icate, but also occurring of various dimensions ; faces of 



