ALTERATION OF THE EARLIER ANDESITE. 229 



potassium silicate, a little potassium carbonate and water. Analysis showed that 

 this mineral had the composition of adularia mixed with a little quartz. The 

 feldspar crystals were sometimes of the ordinary orthoclase habit, and sometimes of 

 the adularia habit." The same investigators obtained orthoclase crystals by heating 

 potash, silica, and muscovite in water in the same apparatus as mentioned above, 

 and at the same temperature. 



Calcite, in rhombohedral crystals, it may be remarked,* was also obtained 

 under similar conditions (temperature 500 C.) by heating precipitated calcium 

 carbonate and calcium chloride with water for ten hours. 



ADULARIA AS A META.MORPHIf MINERAL. 



Apart from the primary orthoclase in igneous rocks, secondary orthoclase, 

 due beyond question to attenuated watery solutions, distinct in every way from 

 rock magmas, has been often described as occurring in, nature. Van Hise* 1 showed 

 that clastic grains of orthoclase in sandstones on the north shore of Lake Huron 

 had been enlarged by a secondary similarly oriented growth. In St. Gotthard, 

 in the Alps, little druses in a fine-granular quartz-albite rock contain clear crystals 

 of adularia intercrystallized with calcite, both of which are younger than the 

 constituents of the rock. In some cases the adularia is provedly younger than 

 the calcite, and in one case it incloses older calcite and chlorite both water- 

 formed minerals showing that the feldspar originated as a precipitate from 

 solution. a In Chester County, Pa., orthoclase occurs in dolomite, indicating 

 that no intense heat was present at its formation. d In the metamorphosed zones 

 near the contact of intrusive igneous rocks it is frequent, as was shown by 

 Allport, and later by Teall," to be the case in altered lower Silurian slates in 

 England, and by Lessen in the Harz. 



ADULARIA IS VEINS. 



Adularia as a gangue mineral in veins has also been described a number of 

 times. In a vein in the Herzog Ulrich mine at Kongsberg, in Norway, Hausmann* 

 found adularia with quartz, pyrite, and dolomite. In veins in Schenmitz, in 

 Hungary, Wiser* found crystalline adularia associated with quartz, dolomite, pyrite, 

 chalcopyrite, blende, and gold. In the Lake Superior copper mines orthoclase 

 occurs in veins, associated with calcite and native copper; the feldspar, like the 

 other minerals, is plainly formed in the wet way, and was deposited later than 

 the copper and the calcite. Adularia occurs also in several places of special 



a Bull. Soc. francaise de min., vol. 4. 1881, pp 171-175. Chemisches Centralblatt, 1892, vol. 1, p. 865. 

 bin connection with the occurrence of calcite and adularia in the same veins at Tonopah. 

 eCited by Zirkel. Lehrbuch d. Petrographie, vol. 1, p. 243. 

 d Bischof, Gustav, Chemische Geologie, vol. 2. p. 401. 

 'Cited by Bischof, Chemische Geologie, vol. 2. pp. 898-399. 



