Essentials for the microscopical determination of rock-forming minerals and rocks; in thin sections - Softcover

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 edition. Excerpt: ...It occurs in leaves and plates, and usually shows hour-glass structure. Pleochroism may be rather weak or wanting, c = yellowish green, colorless, b = blue, a = olivegreen. Cleavage (001) good. The low double refraction and high relief, as well as the mode of occurrence, separate it from all other minerals. Zoisite has parallel extinction, different color, and smaller optic angle. Clinozoisite has different cleavage (001:100 = 6437'), and usually abnormal interference colors. Staurolite occurs in crystalline schists as a contact or dynamo-metamorphic mineral. Inclusions symmetrically arranged or in subparallel bands are common. The yellow, red, or brown color, the pleochroism, c = red-brown, a and b = yellow, the parallel extinction, the large optic angle, 2V = 89, giving a straight bar in sections at right angles to an optic axis, separate it from other minerals. Andalusite is negative and has different pleochroism, g e d r i t e has smaller optic axial angle (2V = 57-79) and amphibole cleavage, anthophyllite has amphibole cleavage and is rarely pleochroic in thin sections, vesuvianite has a pale yellow color, is negative, and has lower birefringence. Clinochlore, one of the chlorites, occurs in leaves, scales, plates, or leafy aggregates as a mineral of schists and serpentines, and as a secondary mineral in igneous rocks from the alteration of ferromagnesian silicates. 2E = 32-90, c:c=--2 to--9, maximum birefringence = 0.011. Pennine is ( = ), 2E = 0-61, has parallel extinction, and the maximum birefringence is 0.002. Spodumene has typical pyroxene cleavage, extinction c:c=--23 to--26, is generally nonpleochroic unless the sections are thick, when a = amethyst, b = amethyst, c = colorless. In many cases it is altered to a mixture of albite and...

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