148 



Case 98. Mica.. — Silicate of alumina, potash, iron, magnesia, &c. — 

 Another group of minerals with variable composition. Mica 

 possesses a most perfect cleavage, by means of which sheets of 

 large size and extreme thinness may be readily split off. The 

 cleavage flakes are perfectly elastic. Por specimens of com- 

 mercial mica see cases 105 and 132 (page 132), 



Muscovite. Potash Mica. "West Australia, Ontario (green variety), 



Canada, Broken Hill. 



867, Russia : a crystal showing the characteristic six-sided 

 form. 



liotite. 

 Zinnwaldite. 



Uranium mica. 



PMogopite. 



I'uchsite. 



Xepidolite. 

 Olivine. 



Serpentine. 



Picrolite. 



Magnesia Mica. Canada, Norway. 



A lithia variety of biotite. Saxony. Londonderry Mica Mine, 

 Coolgardie. 



Saxony. 



Eussia, Canada. 



Chrome Mica. ISTew Caledonia, New Zealand, Eussia. 



Lithium Mica. A beautiful rose-coloured variety. 



Silicate of magnesia with more or less iron. A mineral fre- 

 quently found in crystals or granular aggregates in basalt. BuUi, 

 Walcha, Inverell. 



9034, in case 143: a block of basalt from Bulli, containing 

 large masses of olivine and of hornblende. 



Hydrated silicate of magnesia, resulting usually from the 

 alteration of olivine, but sometimes of pyroxene and amphibole, 

 as is frequently the case in New So nth Wales. Serpentine is of 

 verv common occurrence; it generally occurs intimately associated 

 with other substances as a rock rather than as a mineral. It is 

 sometimes used for ornamental purposes (see page 98). Corn- 

 w^all (red variety from the Lizard), Gundagai, Port Macquarie. 



A fibrous form of serpentine. Gundagai, Goulburn, New- 

 bridf^e, Lucknow, Orange (Carangera Copper Mine). Other 



