Sec. III, Ch. 10: The Opal

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	220 The Opal.

	notable too, that the Opal forms curious pseudomorphs and sometimes takes the form of shells, belemnites, reptilian bones and fossil-wood. Another Opal locality in New South Wales, is at Rocky Bridge Creek, where the mineral occupies the cavities in a decomposed vesicular lava, of andesitic type. It should be noted that Australia occasionally sends us Black Opals, which in some cases are very beautiful, exhibiting variegated colours on a black ground. Opal is also recorded from New Zealand, but this locality is of no commercial importance.

	MEXICAN AND HONDURAS OPALS. Opal is found in several localities in the State of Queretaro, especially at Esperanza, about 10 leagues northwest of San Juan del Rio, Here the Opal has been extensively worked in porphyry, and some of the material from these mines displays a good deal of fire. The Mexican "fire Opal" is obtained chiefly from the porphyry of Zimapan. Opal also occurs in Honduras, in the Department of Gracias, and in Guatemala. Most of this Central American Opal is more transparent and less fiery than that from Hungary, but the conditions of its occurrence seem to be very similar in the two localities. It occurs in veins running through rocks of trachyte. The Honduras Opal is apt to lose its colour, and very little of it comes into the market. Opal is also recorded from Crooke Co., Oregon.

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