THIRDLY.
A stone of the same kind with the last, but streaked with numerous, parallel, slightly tortuous, white lines of the thickness of hairs. These white lines are more crystalline than the parts between them; and the stone splits along them: they frequently expand into exceedingly thin cavities, which are often only just perceptible with a lens. The matter forming the white lines becomes better crystallised in these cavities, and Professor Miller was fortunate enough, after several trials, to ascertain that the white crystals, which are the largest, were of quartz (Professor Miller informs me that the crystals which he measured had the faces P, z, m of the figure (147) given by Haidinger in his Translation of Mohs; and he adds, that it is remarkable, that none of them had the slightest trace of faces r of the regular six-sided prism.), and that the minute green transparent needles were augite, or, as they would more generally be called, diopside: besides these crystals, there are some minute, dark specks without a trace of crystalline, and some fine, white, granular, crystalline matter which is probably feldspar. Minute fragments of this rock are easily fusible.