Minerals in Rock Sections; The Practical Methods of Identifying Minerals in Rock Sections with the Microscope (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1898 edition. Excerpt: ... when strongly heated. Chrysolite is decomposed by hydrochloric and sulphuric acids, with separation of gelatinous silica. H., 6.5 to 7. Sp. gr., 3.3 to 3.4. Hyalosiderite (a more ferruginous chrysolite) and Fayalite (Fe2Si04) are reddish in sections, and common in the basic porphyritic eruptive rocks. IOLITE, Cordierite, Dichroite. Anisotropic. Biaxial. Orthorhombic. Composition: Mg3(Al.Fe)6Si 028. f=a. Elongation 0'. Usual Appearance in Sections: Grains, more rarely pseudo-hexagonal prisms. Twinning may occur and some basal sections show penetration twins. Colorless, but may be bluish in thick sections. Relief low (-'= 1.536), like quartz. Cleavage very variable, parallel to brachy pinacoid 00Poo (010), especially noticeable when decomposition has taken place. Irregular cracks often seen filled with a yellowish substance. Inclusions of sillimanite, zircon, green spinel, etc, characteristic. Pleochroism usually not observed, but may be quite strong in thick sections from prism zjne (yellowish-white c to blue). Pleochroic halos, surrounding inclusions, common and bright yellow in color. Crossed Nicols: Double refraction weak (7--0 = 0.007 to 0.010), like quartz. Interference colors middle 1st order, white to yellow. Extinction parallel to cleavage cracks. In convergent light axial angle large (hyperbolas only seen without ellipses); optical character ( + ). Alteration: Takes place readily, forming mica like decomposition products, the decomposition commencing along the crevices. Differentiation: From Quartz by observation in convergent light, by presence of decomposition along the crevices and by pleochroism in thick sections. The section can also be treated with hydrofluosilicic acid, when the evaporated solution yields...