17 



scrapes nearly to white dust, viz. light yellowish brown, not 

 much unlike rosin, which gives a whitish dust. The splen- 

 dent black crystals are generally grouped as well as con- 

 fusedly crystallized, showing their brilliant polished facets 

 one at a time occasionally very distinctly, but in the group 

 are merely jumbled masses. As they often form among 

 white Quartz, they are the more richly relieved ; and the 

 present specimen is additionally so, by the peculiarity of 

 some of the Quartz, which is found to be, when examined, 

 beautifully crystallized in relieved six-sided crystals, termi- 

 nated at each end by six-sided pyramids, but they are again 

 covered by an opaque, very white, almost mealy coat ; or 

 perhaps, having been acted upon externally, have become 

 opaque by a division of the particles, which on that account 

 are so separable as to be scraped with a steel blade of a knife. 

 Specimens with a thin coat of Chalcedony next to the 

 Blende, and transparent Quartz above it, are less rare. 



TAB. CCCXCVJII. 



1 he 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 tetraedrons, 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 after the Fluor was gone, Galsena 

 or Sulphuret of Lead has formed in a scattered manner about 

 it. This Galsena 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 Galsena originally lay. 



Thus may be seen the changes wrought underground by 

 means of various agents; and thus we have continual proofs 

 of chemical agencv, which perhaps may lead us to inqui- 

 ries that may be of considerable importance, while the sub- 

 ject thus- come to hand is an example too curious to be 

 passed over at a time when investigations drawn from Na- 

 ture are found to be the truest mode of inquiry and im- 

 provement. 



