GOLD. 313 



sparingly in granite, gneiss or mica slate, for the veins of 

 these more highly crystalline rocks are commonly feldspathic 

 or granitic rather than quartzose, and granitic veins seldom 

 afford gold, i The quartz veins often intersect the slaty rock$ j 

 in great numbers, are generally very irregular in size, and J 

 often lie as beds conformable to the lamination. The quartz 

 is frequently rather cellular, containing cavities in which it is 

 crystallized. It generally contains more or less pyrites, and 

 sometimes galena and other minerals. The decomposition 

 of the pyrites leaves the quartz very cavernous, and some- I 

 what rusty in appearance ; and occasionally a little sulphur ; 

 lines the cavities, derived from the removed pyrites. . 'Fhe""l 

 rock in this cavernous state, (as it is very liable to be near \ 

 the surface,) is rather easily quarried out; but deep below, 

 where the minerals are not removed by decomposition, 

 mining is far more difficult. 



The pyrites itself is nearly as hard as quartz, when un- 

 altered, and readily strikes fire with a steel. This pyrites 

 is often very abundant, and contains throughout it consider- 

 able gold ; but the gold is so finely distributed, that little of 

 it can be removed by the ordinary process of crushing and 

 amalgamation, and nature's way of decomposing the pyrites 

 and thereby making it drop its load, is the only effectual one. 

 This is accomplished by exposing the pyrites in heaps, with % 

 moisture and perhaps a little heat, by which it changes to 

 copperas, which may be dissolved and the gold obtained. 

 The galena of a gold region is also usually auriferous. 



Gold sometimes occurs in the slate rocks adjoining the 

 veins, though mostly confined to the latter. The quartz may 

 contain gold when none is visible to the naked eye. 



The minerals most common in gold regions are platinum, 

 iridosmine, magnetic or titanic iron, iron pyrites, galena, 

 copper pyrites, blende, tetradymite, zircon, rutile, heavy spar ; 

 also in some cases, brookite, monazite and diamond. Pla- 

 tinum and iridosmine accompany the gold of the Urals, 

 Brazil and California; and diamonds are found in the gold 

 region of Brazil, and occasionally in the Urals and Eastern 

 United States. 



Gold is widely distributed over the globe. It occurs in 

 Brazil' (where formerly a greater part of that used was ob- 

 tained) along the chain of mountains which rans nearly par- ! 

 allel with the coast, especially near Villa Rica, and in th+> j 



