MATRICES OF VEINS. 



to form the matrix of a mineral vein. The matrices are 

 chiefly quartz, fluor spar, and calc spar ; generally quartz. 

 (See Chap. VII.) 



Fluor spar (fluate of lime) is favourable for lead and 

 copper, calc spar for lead and silver ; but quartz is very 

 nearly the universal matrix of veins in a mineral country, 

 and thus it is that quartz rock should be especially searched 

 for. Very frequently the pieces of quartz broken away from 

 the lode and also the surface portion of the lode are honey- 

 combed. Having been exposed to the influence of the 

 atmosphere and moisture, most of the metalliferous parts 

 once existing in the cavities, and similar to what one might 

 expect to find a few fathoms downwards on the vein, have 

 been decomposed, and so, instead of filling up the honey- 

 comb cavities of the surface quartz, have merely left traces 

 in the form of stains. This only applies to the metallic 

 portions oxidizable, for it is in the surface of honeycombed 

 auriferous rock that the unmistakable yellow specks may be 

 seen in the cells once filled up with iron or copper pyrites 

 or other metallic compound associated with the precious 

 metal. Gold and silver in the native state (the former very 

 much more so than the latter, which becomes tarnished) 

 weather the effects of the elements much better than most 

 metals, and can be recognised in the native condition ; but 

 experience alone can acquaint one with the variously shaded 

 blacks, reds, greens, browns, greys, &c., which the metallic 

 sulphides have left behind as oxides and carbonates. One 

 of the best surface indications is the honeycombed rock 

 brown with iron oxide. In the German mining districts 

 there is a saying 



" Es thut kein gang so gut 

 Er hat einen eisernen hut.*' 



(" There is no lode so good as the one which has an iron 

 hat.") And this quite corresponds with the French " cha- 

 peau de fer," and the Cornish "gossan." 



The iron oxide is really the result of the decomposition of 

 iron pyrites; and in the lode with this at "grass roots," 

 iron pyrites would be found deeper down. Having thus 

 traced the honeycombed quartz the pieces of which are 



