Elements of mineralogy, crystallography and blowpipe analysis from a practical standpoint .. . ^ Physical Characters.—Essentially as in orthoclase. Sp. gr. to , and cleavage at 89° 30 instead of 90°. Before Blowpipe, Etc.—As for orthoclase. Remarks.—Includes varieties, Amazon stone, perthite, chesterlite, etc., formerly grouped under orthoclase. Often interlaminated wiih albite or Anorthoclase. A triclinic sodium-potassium feldspar found mainly in the lavas ofPantellaria. Color, lustre and hardness the same as for other feldspars. Cleavageclose to 90°. Sp. gr., Dist
Elements of mineralogy, crystallography and blowpipe analysis from a practical standpoint .. . ^ Physical Characters.—Essentially as in orthoclase. Sp. gr. to , and cleavage at 89° 30 instead of 90°. Before Blowpipe, Etc.—As for orthoclase. Remarks.—Includes varieties, Amazon stone, perthite, chesterlite, etc., formerly grouped under orthoclase. Often interlaminated wiih albite or Anorthoclase. A triclinic sodium-potassium feldspar found mainly in the lavas ofPantellaria. Color, lustre and hardness the same as for other feldspars. Cleavageclose to 90°. Sp. gr., Distinguished by its optical characters. ALBITE.—Soda Feldspar, Pericline. Composition.—NaAlSigOg. General Description.—Pure white,, granular, masses or instraight or curved laminae. Less frequently in white or colorlesstriclinic crystals, usually small. SILICA AND THE SILICATES. 355 Crystallization.—Triclinic. Angles a = 94° 3; /9=ii6°29; 7-= 88° 9. Axes ^ : 1^ :c = : I : Simple forms,Fig. 588, usually show both hemi prisms 7mLnd -Af, base c, brachypinacoid d and other modifying planes. Angles mM= 120 46;C7H= 114° ] cM= 110° 50; bm= 119 34. EiG. 588. Fig. 589. Fig. 590.
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