Olivin, or Chrysolite

The specimen from which the upper figure in the gangue is taken, was lent me by G. B. Greenough, Esq. It is brought from Inimore in the Isle of Mull. It contains one large well characterized mass, showing the direction of the planes of the nucleus at right angles; the cross fracture conchoidal; its usual greenish yellow colour, and some ochraceous stains, produced by partial decomposition. The gangue is as usual. Basalt, The little nodules below comprehend most of the varieties in colour from the yellowish to the olive green, whence its name. I was favoured with these from Scotland by Professor Jameson; the rock in
which they were found has decomposed; it was probably of the same nature as that of the upper figure. Some of these are more or less mixed with the blackish green nearly opaque grains of the same substance. The outline shows the form in which it sometimes crystallizes, (the variety named subdistique by Haüy,) including the nucleus, which appears to be a rectangular prism.

The lighter and yellower green varieties are generally most splendent, and those of a darker tint less so. Olivin sometimes decomposes in the hollows of Basalt, when its surfaces become more or less iridescent, and are coated by a yellowish or reddish Oxide of Iron. It is brittle, and cannot be scratched with a knife, in the unchanged state. It is nearly infusible without a little borax, with which it melts into a dark green globule. Nitrous acid dissolves the Iron which colours it. Spec. Grav 3.225 to 3.265.

By analysis it is found to contain