A popular guide to minerals : with chapters on the Bement Collection of minerals in the American Museum of Natural History, and the development of mineralogy . Fig. 292 Fig. 293 To produce color effects more strikingly in such sections, platesof quartz or gypsum are introduced above them in the convergent light the elementary crystals may display axial fig-ures (Fig. 293, aragonite). Mica films piled on each other, successively reversed in posi-tion, yield an uniaxial effect with the black cross and the color rings,although mica is biaxial. Double Refraction is developed in amorp
A popular guide to minerals : with chapters on the Bement Collection of minerals in the American Museum of Natural History, and the development of mineralogy . Fig. 292 Fig. 293 To produce color effects more strikingly in such sections, platesof quartz or gypsum are introduced above them in the convergent light the elementary crystals may display axial fig-ures (Fig. 293, aragonite). Mica films piled on each other, successively reversed in posi-tion, yield an uniaxial effect with the black cross and the color rings,although mica is biaxial. Double Refraction is developed in amorphous bodies, as glass,by pressure and torsion, and anomalous double refraction in isotropiccrystals has been referred to internal strain. Fluorescence is an optical property of minerals especially wellshown in Fluorite. Cornish fluorites in transmitted light appearsea-green, while in reflected light they are a beautiful violet-blue. DEFINITION OF TERMS 85 Thus in a darkened room such a specimen is illuminated, by a rayof light allowed to fall upon it, with a blue color, which howeverceases at a moderate depth, within the crystal, and the light thuspassi
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmineral, bookyear1912
