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Ch. 1: Form of Minerals

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	FORM OF MINERALS.	41

	system. Thus dihexagonal pyramids are produced with the general sign mPn, the chief peculiarity being that, whereas in the tetragonal system η might have any rational value from 1 toin the hexagonal system it can only vary from 1 to 2, in consequence of the geometric character of the figure. When n=2 the dihexagonal changes into an hexagonal pyramid of the second kind, whose sign is »iP2. When m isvarious prisms arise from similar changes in the value of η ; and when m=0, the basal pina-coid. Few hexagonal mineral species form perfect holohedric combinations. Though quartz and apatite appear as such,



	yet properly the former is a tetartohedral, the latter a hem-ihedral species. In holohedric species the predominant faces are usually those of the two hexagonal prisms ooP andor of the pinacoid OP ; while the pyramids Ρ and 2P2 are the most common subordinate forms. Figure 38 represents the prism, bounded on the extremities by two pyramids ; one, P, forming the point, the other 2P2, the rhombic faces on the angles, orΡ . 2P2. In some crystals the lateral edges of the prism are replaced by the

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Feuchtwanger. Treatise on Precious Stones.

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1 Page 399 second in August and September; and the more rain, the more
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2 Page 401 weight of twenty-four grains is counted as thirty; so that a
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3 Page 398 body on, or by boring a hole in, the shell. The Chinese are
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4 Page 400 At the Pearl Islands, near the Isthmus of Panama, the pearl
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5 Page 406 In 1620, King Philip IV., of Spain, purchased a pear-shaped
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6 Page 401 weight of twenty-four grains is counted as thirty; so that a
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7 Page 402 reach the age of seven or eight years, and in the fourth yea
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8 Page 403 found in the Elster river, in the kingdom of Saxony, from it
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9 Page 404 nearly two millions of francs ; Julius Csesar presented to S
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10 Page 404 nearly two millions of francs ; Julius Csesar presented to S
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11 Page 405 The seed pearls, when quite round, are worth about one hundr
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12 Page 411 and on the Continent ; around Southampton, in England, these
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13 Page 412 Artificial Pearls. Artificial pearls or beads are of variou
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14 Page 406 n 1620, King Philip IV., of Spain, purchased a pear-shaped p
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15 Page 409 near the town of Paterson, New Jersey, went to a neighbori
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16 Page 410 of Messrs. Tiffany & Co., was purchased from Mr. Howell for
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17 Page 415 The shad-fish, as well as the white-fish of our lakes, must
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18 Page 413 decomposition, and for their preservation numerous chemica
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19 Page 414 Heidelberg, Nuremberg, Sonnenberg, Meistersdorf, in Bohemi
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