. Elementary physics and chemistry: first stage. Science. CRYSTALS AND CRYSTALLISATION. 125 REASONS AND RESULTS. Crystals.—When substances are found in lumps hav regular shape, which is always the same for the same kind of thing, it is said to be found in crystals, or to be crystalline. Generally the shapes which crystals have are well- known forms in geometry. Thus some crystals are known which are perfect cubes (Fig. 88), such as crystals of rock-salt, fluorspar, iron pyrites. Sometimes the crystal has eight sides, like the solid known as the octahedron (Fig. 85). The diamond is sometimes fo
. Elementary physics and chemistry: first stage. Science. CRYSTALS AND CRYSTALLISATION. 125 REASONS AND RESULTS. Crystals.—When substances are found in lumps hav regular shape, which is always the same for the same kind of thing, it is said to be found in crystals, or to be crystalline. Generally the shapes which crystals have are well- known forms in geometry. Thus some crystals are known which are perfect cubes (Fig. 88), such as crystals of rock-salt, fluorspar, iron pyrites. Sometimes the crystal has eight sides, like the solid known as the octahedron (Fig. 85). The diamond is sometimes found having this shape. Rock-crystal has gene- rally six sides, and a pyra- mid at one or both ends (Fig. 84). When you get on farther with your study of science, you will learn that crystals can all be divided into six classes, every member of each class or family having something about ^no^nc^^ys^aUineSbstance.' its shape the same. ?, photograph by Mr. '^ Hadley.). a com- (PVom H. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Gregory, R. A; Simmons, A. T. London: MacMillan
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