SILK ATI. S. TITANATKS, ETC. 40!) 



Uses. Orthoclase is quarried in Maine, Massachusetts, Con- 

 necticut, Pennsylvania, and Maryland from the pegmatites, where 

 it i> a-M.ciated with quart/, inuscovite, and small quantities of mag- 

 netite. tourmaline, and garnets. It is ground and mixed with kao- 

 lin and quart/ in llie manufacture of chinaware. It is also a com- 

 ponent of both the gla/e and undergla/e. It is also the flux used 

 in the making of corundum wheels. It is used as a wood filler; 

 in scouring soaps ; and in opalescent glass. Artificially orthoclase 

 has not been formed by the dry fusion of its components, but 

 other chemical reagents which act as liquefiers must be added, as the 

 alkalic feldspars are so viscous at their fusing points as to prevent 

 crystalli/ation in any moderate length of time. If fluorides, tung- 

 states, or magnetite are added to the melt, or if heated in the pres- 

 ence of water under pressure, crystals are formed. 



MICROCLINE 



Microcline. KAlSi 3 8 ; A triclinic form of potassium alu- 

 minium trisilicate in which the cleavage angle varies by 30' from 90, 



FIG. 459. Section of a Complexly Twinned Feldspar between Crossed Nicols. 



or the angle 010 A 001 = 89 30'. In all other respects it is very 

 much like orthoclase. Their difference may be seen in the table, 

 page 404. 



