Sec. IV, Ch. 1: Semi-Precious Stone, Agate

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	CHAPTER I.

	THE AGATE.

	Y the term Agate, the mineralogist understands a composite substance, an association of certain siliceous or quartz-like minerals, which in texture, colour, and transparency are diverse one from another. These Agate-forming minerals are chiefly Chalcedony, Carnelian_s Jasper and Quartz. Two or more of these, forming a variegated stone, and usually presenting a diversity of spots and stripes, may be denominated an Agate. The name is derived from the river Achates, in Sicily, now known as the Drillo, in the Val de Noto, wherein, according to Theophrastus, the ancient Agates were found, in his time. The Agate is occasionally found in veins, as in certain localities in Saxony and Bohemia, but, as a rule, it occurs in the form of nodules embedded in an amygdaloidal rock, more or less akin to basalt. On the decomposition of the amygdaloidal agate-bearing rock, the enclosed Agates, by reason of their resistance to the disintegrating effects of weather, remain behind as nodules ; hence Agates are frequently found loose in the beds of rivers. The " Scotch pebbles "are Agates which have been liberated by decomposition of their matrix of porphyrite, and are found scattered over the surface of the ground.

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