THE FAMILY OF FELSPARS. 



NAME. 



Orthoclase 



San i dine 

 Adularia 

 Albite 



Oligoclase - 



Labradorite 

 Anorthite 



Andesine 

 Nepheline 



Leucite 



COMPOSITION. 



Double silicate of alumina 

 and potash, with a little 

 soda 



A grey and glassy variety 

 of orthoclase, usually with a 

 little lime and magnesia 



A nearly transparent variety 

 of orthoclase with a little 

 lime 



Double silicate of alumina 

 and soda. Usually asso- 

 ciated with orthoclase 



Double silicate of alumina 

 and soda, in which the 

 soda is partly replaced by 

 lime and potash 



Double silicate of alumina 

 and a compound of soda 

 and lime. Usually with a 

 little iron. Dissolves in hot 

 hydrochloric acid 



Double silicate of alumina 

 and lime, in which the 

 lime is partly replaced by 

 small quantities of soda, 

 potash, or magnesia. Usu- 

 ally a little iron. Dissolves 

 in hydrochloric acid 



A grey, green, or red double 

 silicate of alumina, and a 

 compound of soda and lime, 

 usually with some potash 

 and a little magnesia. 



A white or coloured double 

 silicate of alumina, and a 

 compound of soda and 

 potash. Dissolves in hy- 

 drochloric acid 



Ash-grey colour, in 24-faced 

 trapezohedrons, but belongs 

 to the tetragonal system. 

 Is a double silicate of alu- 

 mina and potash. Dissolves 

 in hydrochloric acid 



ROCKS IN WHICH FOUND. 



Granite, syenite, porphyry. Is 

 green from containing copper in 

 some of the rocks 'of South 

 America and Colorado. 



Trachytes, phonolites, pitchstones, 

 obsidian. 



Granite of St. Gothard. 



Trachyte of Pantellaria, miascite 

 of Miask in Siberia, granite of 

 the Muorne Mountains, and in 

 various granites, greenstones, and 

 gneiss, though not as a chief 

 constituent 



In granite of many places in 

 Sweden and Scotland, in gneiss 

 near Freiberg, in syenite, the 

 Verde - Antico porphyry of 

 the Morea, the trachytes of 

 Teneriffe, and in diabase and 

 diorite. 



In the gabbro of Skye, in all 

 basalts, dolerites, hypersthenite, 

 older lavas of Etna, &c. 



Old lavas of Monte Somma, 

 Thjorsa in Iceland, napoleonite 

 of Corsica, diorite of Harzburg, 

 syenite of Carlingford. 



Occur in gneiss in Scotland, in the 

 Andes combined with hornblende 

 forming andesite, also in syenite 

 of the Vosges. It resembles 

 oligoclase. 



In basalt and dolerite, in mias- 



In basalt and dolerite, in mais- 

 cite and zirconsyenite ; in dole- 

 rite it occurs in short thick 

 hexagonal columns ; at Vesu- 

 vius and near Rome in lavas, in 

 phonolite as in the Wolf Rock 

 on the Cornish coast. 



Unknown in the older rocks. 

 Monte Somma lavas of Vesu : 

 vius. trachyte between An- 

 dernach and Laach, dolerite 

 of the Kaiserstuhl in Baden. 

 At Bohmisch-Wiesenthal in the 

 Erzgebirge leucite crystals are 

 changed into orthoclase. 



