CATALOGUE OF MINERALS. 19 



Fused, more or less highly, and in combination with feldspar and other min- 

 erals, producing quartzite, feldsite, jasperite. obsidian or volcanic glass, one form 

 of which is pumice, which may be ground into ashes or volcanic dust. 



From being held in solution in water quartz often fills rock cavities and fis- 

 sures, entering them from above, and thus may enclose other minerals like pyrite, 

 garnets, epidote, etc., or metals like copper and gold. 



From being held in solution quartz also often fills the cavities in rocks 

 once occupied by the crystals of other minerals but which have been dissolved away, 

 leaving a mould of their form, and then the quartz assumes a crystalline form not 

 its own, but that of the mineral of which it took the place. This change may 

 have iaken place gradually as the dissolving mineral disappeared. In a like man- 

 ner quartz sometimes fakes the place of decaying wood, shells of mollusks, coral, 

 or other organic structures, often reproducing their forms with perfect exactness; 

 tHs exact reproduction is particularly noticeable in the case of wood in which the 

 cells and grain are to be seen. Such reproductions of organic structures are call- 

 ed, rather incorrectly, petrifactions, but are more correctly termed pseudomorphs, 

 which means false forms. It is usual to designate the form assumed by the 

 quartz as quartz pseudomorph after the crystal, of organic structure. Thus, for 

 example, we may find quartz pseudomorph after pyrite, calcite, etc., or quartz 

 pseudomorph after wood or coral, etc. 



In the arts pure crystalline quartz has been used as lenses for eyeglasses, mi- 

 croscopes, etc., and also in this form, or when colored in the chemical series or as 

 agates, in jewelry. Primitive man used quartz in its various forms, pure and 

 impure, as implements and weapons. In both ancient and modern art it enters 

 largely into the composition of glass and from some of its combinations, as in the 

 sandstones and granite, are produced excellent building stones. Quartz in man y- 

 of its forms is well illustrated in the collection. 



Those desiring particular varieties of quaitzlike Gold-bearing, Iron-stained, 

 Drusy, Smoky, Amethyst, Massive, Crystaline, etc., will please designate the 

 variety they require 



Quartz Amethyst 252 456. 



" Altered 265 272-73. 



44 Calcite 445 



44 Crystal 211-16 250255 268 277 282 285 1093. 



44 Drusy 221 276. 



" with Galenite 186 190-92 197 200. 



4i Granular 263. 



" Geode 209-0-7-02. 



44 Garnet 692. 



44 Gold-bearing 279. 



44 Massive and Garnet 502 689. 



" Iron-stained 253 257 260 267-69 71 75 77 83 84 88. 



