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Ch.14: Apatite - Jet

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	PRECIOUS STONES. 287

	a hydrous sulphate of calcium, CaS0₄, 2H₂0. It occurs frequently in connection with sedimentary deposits laid down in closed areas of water ; Alabaster is often found in irregular beds, and Satin Spar in veins, in marls with such a history, as in those in Cumberland, Westmorland and Nottingham. Very fine massive Gypsum is found at



	Castelino, 35 miles from Leghorn. Fig. 42 shows a vein of Satin Spar. Amber. Amber is not strictly speaking a mineral, being of organic origin. It is found in irregular masses of a yellow brown or reddish shade, showing a conchoidal fracture but no cleavage. It is transparent to translucent and opaque, with a specific gravity of 1.05 to 1.10, and a hardness of 2 to 2-1/2; the lustre is resinous. On heating it softens and then melts. The ancients, who called Amber Eleetrum, noticed

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