Minerals in rock sections; the practical methods of identifying minerals in rock sections with the microscope, especially arranged for students in technical and scientific schools . fromwhich it may be distiiiguislicd by not being so easily attacked bycold dilute acid (test can be made on slide with cover off), by ten-dency towards crystalline boundaries, by absence of twin lamellae(or when present parallel to — 2/?(o2 2i), hence about parallel toshorter diagonals of cleavage rhombs), and by micro-chemicaltests. The distinction at times may be very difficult. Remarks : Occurs in sedimentary fo
Minerals in rock sections; the practical methods of identifying minerals in rock sections with the microscope, especially arranged for students in technical and scientific schools . fromwhich it may be distiiiguislicd by not being so easily attacked bycold dilute acid (test can be made on slide with cover off), by ten-dency towards crystalline boundaries, by absence of twin lamellae(or when present parallel to — 2/?(o2 2i), hence about parallel toshorter diagonals of cleavage rhombs), and by micro-chemicaltests. The distinction at times may be very difficult. Remarks : Occurs in sedimentary formations and as crystals in limestone and otherrocks. In certain rocks the dolomite crystals may not have a very good bond, anda drusy structure may also be characteristic of the spaces between dolomite crystalsin rocks. Only slightly attached by cold dilute acids, but if acid is heated it dissolveseasily with effervescence. APATITE. Anisotropic. Uniaxial. Hexagonal. Composition: Ca,()(PO,)3. r= a. Elongation || Appearance in Sections: Minute, slender, hexagonal prisms, cross-sections having regular hexagonal boundaries, needles, and grains. Figs. 14 a and Fig. 42. —Apatite, showing cross fracture, in nepheline-basalt. (From Cohen.) Color. — Generally colorless, seldom bluish or brownish (onlyin eruptive rocks). Index of Refraction.—//= , hence relief more markedthan that of the colorless associated minerals. Cleavage. — Seldom observed microscopically. Parting. — Long columnar crystals generally show a transversejointing, so that the pieces may be more or less 66 CHARACTERS OF MIXERALS. I)iclitsio)is. — (ias and fluid ma}- be Light: Plcochroism. — None shown b\- the colorless crystals, the coloredcrystals show stronger absorption parallel to c. Crossed Nicols: Double Refraction. — Weak (j- — (/. = ). Interference Colors.— The lower first order, generall} grayish-blue or white. Extinction.—As apati
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