. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. Fig. 78. Crystalline form of epidote. axis of symmetry, that is to say, perpendicular to the single plane of symmetry. Owing to â the predominance of one pair of parallel faces of the prism the crystals usually present a flattened appearance. The elongated prism-faces are very often distinctly striated parallel to their length, that is to say, para
. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. Fig. 78. Crystalline form of epidote. axis of symmetry, that is to say, perpendicular to the single plane of symmetry. Owing to â the predominance of one pair of parallel faces of the prism the crystals usually present a flattened appearance. The elongated prism-faces are very often distinctly striated parallel to their length, that is to say, parallel to their mutual intersections, while the small terminal faces of the crystals are usually smooth. It frequently happens that two such prismatic crystals grow together in twin position, and when this is the case some of the terminal faces then form re-entrant angles with each other. As a rule, terminal faces are developed at only one end of the crystal, the other being attached to the matrix. A few of the forms most commonly taken by epidote are represented in Figs. 78a to c; the first two of these, a and b, are simple crystals, the third, c, is a twin-crystal. There is a definite cleavage parallel to one of the prism-faces, and one, rather less definite, parallel to another prism-face. The hardness is 6J, being thus rather less than that of quartz. The specific gravity ranges from 3-25 to 3-5 according to the amount .of iron present. The specific gravity of crystals from the Knappenwand, which are 2d. 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 Bauer, Max, 1844-1917; Spencer, Leonard James, 1870- tr. London, C. Griffin and Company, Ltd.
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