Silvery Mica

In the description of tab. 180, we noticed the difficulty of imitating the lustre of this substance; but having found means of partly surmounting that difficulty, we are happy to produce examples in the present figure. This one is a curious aggregation of laminated crystals, if I may so call them. It is also very remarkable for being one of the first examples of Mica showing an inclination to mackle. In the present instance the plates are chiefly aggregates of smaller rhomboidal ones; the mackle forms by the sides of the rhombs being contrary to each other, like some of the Gypsums. See the lower figure of tab. 223, which seems to depend upon similar laws of crystallization.

This is sometimes found in very large masses. I have specimens six inches long from Aberdeen.—Schorle is occasionally included in it.

I have lenticular crystals of this substance in an ordinary specimen, which, as they certainly are but little if at all noticed, I mention here. They are seemingly formed of the laminæ placed a little irregularly edgewise, resembling the lenticular Sulphate of Barytes and some specimens of Talc, which latter is however generally smaller, see tab. 182, where they nearly approach this figure, or rather in tab. 74, under the name Chlorite: see description, p. 154. I do not doubt, now that it is observed, but that it will be found not unfrequently. The specimen was sent me as gathered near Aberdeen by a dealer without any particular observation, but I could not let it escape unnoticed here. The specimen on the whole is rather dull reddish brown.