260 ANDESITES IN EUROPE. 



times they are more or less decomposed, especially in the andesites of 

 the Stenzelberg in the Siebengebirge. Sanidine is often present. 

 Magnesia-mica occurs in dark-brown or red hexagonal plates, frequently 

 surrounded and penetrated by magnetite. It is usually fresh, always 

 occurs in large plates, and is absent from the ground mass. Horn- 

 blende is usually found in prismatic crystals, either brown or green, 

 commonly green when the rock contains quartz. When hornblende 

 is brown, it is usually surrounded by magnetite ; it then contains ovoid 

 inclusions of glass. The mineral is sometimes decomposed in the 

 greenstone-like dacites. Like mica, it rarely occurs as a part of the 

 ground mass. Augite occurs in small grains and columns as a con- 

 stituent of the ground mass, and also in crystals, but is less abundant 

 than hornblende and mica. It is not decomposed. Quartz occurs in 

 grains and crystals in variable proportion in many andesites. It differs 

 from the quartz of rhyolite, and resembles that of quartz-porphyry in 

 rarely containing glass inclusions ; and it abounds in fluid inclusions, 

 with cubic crystals, except in the Department of Var. 



Tridymite is rare, but is seen in the hornblende-andesite of Dub- 

 nik. Apatite occurs in long colourless needles, and in short crystals 

 tinged blue or brown. It is common in the Stenzelberg in the 

 Siebengebirge, and is always present in the Sengelberg, near Salz in 

 the Westerwald. Titanite is a common accessory mineral in the 

 Siebengebirge, the Department of Var, and Tres Montanas in Canary. 

 Hauyine is characteristic of the andesites of the Canaries. Garnet is 

 found in biotite-andesites near Buda-Pest, and some other Hungarian 

 localities. As products of decomposition, andesites contain opals and 

 chalcedony in Servia and Hungary. 1 



Localities for Andesites. Among the more important European 

 localities for andesites are Shemnitz, Kremnitz, the St. Andra-Visegrad 

 Mountains, near Buda-Pest in Hungary ; the Transylvanian Erzge- 

 birge, the south of Servia, the Smrkouzgebirge in Styria ; at Stary 

 Swietlan, near Banau in Moravia, where the rock abounds in siderite, 

 calcite, and various carbonates. 



In the Auvergne hornblende-andesites are seen in the lava from 

 the Puy de Moutchie, Eigolet-Haut, and Plateau de Durbize, where 

 they make a transition towards trachytes. A rock free from augite 

 occurs in the valley of the Dordogne near Mont Dore. These ande- 

 eites sometimes contain a little crystallised quartz, as at the foot of 

 the Briingelsberg in the Rhondorf Valley, in the Great Breiberg, and 

 at Kelberg in the Eif el ; at the Puy de Chaumont and Liorant in 

 Cantal, and many localities in Hungary, Moravia, and other regions. 



In Italy andesites occur in the Eganean Hills at Monte di Ferro 

 di gran Pietra, Monte della Croce and Teolo. 



In the Andes of Ecuador at Pululagua, the andesite is almost free 

 from augite. A similar rock occurs at Toluca in Mexico, but it con- 

 tains quartz, olivine, hornblende, and biotite. 



Hornblende-andesite is met with in the Caucasus near Kasbek. 



1 Rosenbvusch : Min. Physiog. 



