256 Account of some new Vesuvian Minerals. 
Ausiliary Characters. Texture laminar—the directidii 
of the lamine parallel to the axis of the prism. Ordinary 
colour is brown ; with pearly or opaline lustre. : 
Physical Characters—Sp. gr. 2.25. The lustre is opa- 
line in the transparent crystals, pearly in the opaque. The 
colour is brown in the former, white in the Jatter. The tex- 
ture is laminar, the lamin being paralle] to the axis of the 
prism. ‘The laminz of transparent crystals adhere so close- 
ly to each other, as to give it the appearance of compact tex- 
ture to the naked eye. In the opaque and translucent crys 
tals the laminz are very apparent, and easily separated. 
The transverse fracture is unequal,—-vitreous in the transpa- 
rent and translucent crystal, and dull in the opaque. The 
loncitudimal fracture is laminar. 
he Davina shows double refraction in its laming. 
Chemical Characters. Pulverised and treated with nitric 
acid, at the ordinary temperature, it produces a momentary 
effervescence, (owing to a small quantity of carb. of lime, 
mechanically combined with it,) and then subsides into 4 
yellowish perfect jelly, rather cellular. 
itric acid in which Davina has been digested, dissolves 
e flame of the blowpipe, it melts and forms a cellular 
enamel. With soda, it dissolves imperfectly, and eventually 
forms a globule of opaque enamel. With boracic acid, ex- 
posed on platina wire, it forms a limpid colourless globule. 
With the pecmplorsc salts, in just proportions, it affords 4 
milky opaline globule, which ‘is opaque when warm, but 
