278 DESCRIPTIONS OF MINIOIALS. 



Cleavelandite is a lamellar variety occurring in wedge- 

 shaped masses at the Chesterfield albite vein, Mass. 



Obs. Albite occurs in some granites and gneiss, and. is 

 most abundant in granite reins. Fine crystals occur at 

 Middletown and Haddam, Conn., at Goshen, Mass., and 

 Granville. X. Y. ; Unionville. Delaware County, Penn. 



The name albite is from the Latin alb us, white. 



Microcline. 



A potash -feldspar, very close to the following species in 

 angles, and also in physical characters, and identical with it 

 in composition. But it is very slightly triclinic, the angle 

 between its cleavage planes varying but 16' from 90° ; and 

 hence its cleavage surface shows usually the fine striations 

 exhibited with rare exceptions by all the triclinic feldspars. 

 Colors white, flesh-red, copper-green. The last is what has 

 been called Amazon-stone ; as heat destroys the color it has 

 been supposed to be of organic origin. 



Occurs in the zircon-syenyte of Norway ; also in the Urals ; 

 Greenland; Labrador; Leverett, Mass.; Eedding, Conn.; 

 Delaware ; Chester County, Penn. ; White Mountain Notch, 

 green ; Pike's Peak, Amazon-stone ; Magnet Cove, Ark. 



Orthoclase. — Common Feldspar. 



Monoclinic ; and hence angle between the cleavage planes 

 90°. Figures 1 to 4 represent common forms, and 5 to 8 

 twin crystals. Usually in thick prisms, often rectangular, 

 and also in modified tables. Also massive, with a granular 

 structure, or coarse lamellar ; also fine-grained almost flint- 

 like in compactness. Colors light ; white, gray, and flesh- 

 red common ; also greenish and bluish-white and green. 



Composition. K,A1 16 Si 6 = Silica 64*7, alumina 18*4, 

 potash 16-9 = 100. Soda sometimes replaces a portion of 

 the potash. B.B. fuses with difficulty; not acted on by 

 acids. 



Common feldspar includes the common subtranslucent 

 varieties ; Adularia, the white or colorless subtransparent 

 specimens, a name derived from Adula. one of the highest 

 peaks of St. Gothard. Sanidin or glassy feldspar includes 

 transparent vitreous crystals, found in trachytes and lavas ; 

 but some of the ''glassy feldspar'*' belongs to the species 

 anorthite. Loxorlase is a gravish variety with a pearly or 

 greasy lustre that contains much soda. 



