178 



ALUMINA. 



\ 



Composition: silica 68*5, alumina 19*3, peroxyd of iron 

 and manganese 0*3, lime 0*7, soda 9 1. Acts like feldspar 

 before the blowpipe, but tinges the flame yellow. 



Cleavelandite is a lamellar variety occurring in wedgt- 

 shaped masses at the Chesterfield albite vein, Mass. 



JDif. Albite differs from feldspar in containing a large 

 proportion of soda. It may generally be distinguished when 

 associated with that species by its uniform white color ; also 

 by the form of the crystals, which are more oblique and ir- 

 regular, often tabular, with two of the edges very acute ; also 

 by* the yellow tinge given the blowpipe flame. 



Obs. Albite like feldspar is a constituent of many rocks> 

 replacing feldspar. Albite granite is commonly lighter 

 colored than feldspar granite, arising from the usual white- 

 ness of the albite. j Fine crystals occur at MiddletowrTand 

 HaddaTfi*; Conn^'aY Goshen, Mass., and Granville, N. Y. 



The name albite is from the Latin albus, white. 



Andesine. Triclinic, like albite. H=6. Gr=2-65— 274. Color 

 white, gray, greenish, yellowish, flesh-red. Composition of a specimen 

 from the Andes, silica 59'6, alumina 24*2, peroxyd of iron 1*6, lime 

 58, magnesia 1/1, potash 1*1, soda 6*5=99 92, (Abich). Found in 

 the Andes at Marmato ; in the Vosges, France ; in Canada. 



Anorlhite. Near albite. The form is an oblique rhomboidal prism, 

 P : T=110° 57' T : T=120° 30'. Its crystals are glassy and tabular 

 'n form. H=6. Gr=2"6 — 2.8. Differs from albite in not tinging 

 the blowpipe flame deep yellow, nor affording a clear glass with soda. 

 From Mount Somma, near Naples. 



Bytownite of Thomson, is a greenish-white massive mineral from 

 Bytown, Canada. H=6— 65. ' Gr=27— 2*8. 



(1 



liABRADORITE. 



Triclinic. P : M=W 28', P : T=114° 48, M : T= 

 119 16'. Cleavage parallel with P, nearly per 

 feet ; M distinct. Usually in cleavable massive 

 forms. 



Color dark gray, brown, or greenish brown ; 

 and usually a series of bright chatoyant colors 

 from internal reflections, especially blue and green, with 

 more or less of yellow, red .and pearl-gray. Translucent, 



How does albite differ from feldspar ? What is cleavelandite ? Wh^l 

 fe peculiar in the colors of labradorite 1 Mention other characters. 



