GEOLOGICAL MEMOIRS. 



1 



they are of some importance from their association with metalliferous 

 quartzites. 



The amphibolites, of variable granular texture, and always con- 

 taining some oligoklase, occur in mass, especially around Ob- and 

 Unter-Huip, Milin, and Brezuitz. The diorites accompany them as 

 beds or veins ; and, from the conditions of their association and their 

 transition one into the other, the diorites and the including amphi- 

 bolites appear to have been contemporaneous in their origin. 



The porphyries are all quartziferous and euritic ; the granitic and 

 biotitic varieties are the most extensive ; true euritic porphyries 

 being only subordinate. The last, only locally interspersed with 

 quartz, and frequently composed of unmixed eurite, may be regarded 

 as a compact, finely crystallized variety of stratiform granite. 



Granitic porphyries differ from porphyroid granite only by their 

 fundamental mass being compact and more or less fine-grained. This 

 variety of porphyry, which is met with only in a few localities, is 

 generally associated with micaceous (biotitic) porphyry, characterized 

 by containing exclusively the variety of mica named "biotite." Ac- 

 cording to M. Grailich, the apparent optical angle of the biotite is 

 very small, varying between and 3°. The biotitic porphyries are 

 bedded, with a strike between N.E. and E., and form distinct zones, 

 exclusively confined to the granitic mass, enclosed between two areas 

 of clay-slate, and quite wanting in the rest of the granitic district. 



The metalliferous minerals of the granitic district are not of 

 importance, the working of gold- and silver- ores in the light-coloured 

 bedded granite and the biotitic porphyries having been long since 

 abandoned. At present workings are carried on in the silver-ores 

 and red oxide of iron in the amphibolites of Ober-Lichnitz and Sli- 

 witz, and the antimony- ores of the biotitic porphyry of Mitteschau, 



[Count M.] 



On the Extraction of Silver, Cobalt, and NiCKEL/rom the 

 JoACHiMSTHAL Silver-Ores. By M. Patera. 



[Proceedings Imp. Geol. Institute, Vienna, November 6, 1855.] 



In simultaneously extracting silver, cobalt, and nickel from the 

 rich ores not long since discovered in the Joachimsthal Mines *, in 

 Bohemia, M. Patera first roasts the ore in an atmosphere of aqueous 

 vapour, to prevent loss by the escape of gases and volatilization ; the 

 roasted ore is then placed in wooden tubs and treated with moderately 

 diluted sulphuric acid, mixed with some nitric acid, at a high tempe- 

 rature. Nearly the whole of the silver, cobalt, and nickel is dissolved ; 

 and the solution contains also some iron, copper, and arsenic. The 

 silver is then precipitated by means of a solution of sea-salt ; the chlo- 

 ride obtained, reduced by iron and smelted, gives a silver of great 

 purity. The arsenic is separated by the addition of chloride of 



* See also Quart. Joum. Geol, Soe. vol. xi. part 2, Miscell. p. 37. 



