Sulphuret of Zinc
The various circumstances which attend a mineral are very convenient to be known: I therefore have figured Sulphuret of Zinc in one of its usual scattered appearances, and with the seeming irregular crystallization common to it. It is in tetraëdrons, nearly as the geometrical figure of tab. 74, more or less formed of smaller crystals with little shining facets, or very dull, very different from those fine smooth almost steel-like polished crystals in tab. 397.
I chose the present specimen, as it would elucidate some other subjects if attentively considered. The matrix is chiefly Quartz, which has probably formed over Cubic Fluor, in a very loose and rough manner, as may be seen by the impression; and alter the Fluor was gone, Galæna or Sulphuret of Lead has formed in a scattered manner about it. This Galæna has, however, mostly passed away, and left Brown Pearlspar in thin walls, which, having covered the cubes, are at right angles in the various positions in which the Galæna originally lay.
Thus may be seen the changes wrought underground by means of various agents; and thus we have continual proofs of chemical agency, which perhaps may lead us to inquiries that may be of considerable importance, while the subject thus conic to hand is an example too curious to be passed over at a time when investigations drawn from Nature are found to be the truest mode of inquiry and improvement.