Agate
Posted on June 17, 2008
Filed Under Uncategorized |
This variety is essentially striped, the stripes or bands varying in width and color, according to the conditions present during formation. The stripes may be distinct or faint, but they can generally be seen under a microscope. The differently colored bands may be wide or narrow: a stone examined by Sir David Brewster was found to have over 17,000 definitely marked bands in an area of one square inch. The bands run parallel to each other, straight, wavy, or zig-zag, but they are generally concentric.
Colors may vary within one stone, but they are usually pale, the commonest shades being milk-white, yellowish, reddish, and brownish. Bluish and greenish colors are unusual, and those usually seen in some form of jewelry are almost sure to have been artificially stained. The color may be irregular on account of included impurities. People who buy diamond engagement rings are often interested in agate jewelry also.
Moss agate is not banded, but it contains a varying amount of impurity in the nature of a greenish mineral (oxide of iron or delessite), this often giving fern, leaf, and landscape effects when viewed in the light. These green, moss-like inclusions which give this species its color are not due to moss or any organic substance, as is sometimes thought.
Mocha stone is similar to moss agate, but it contains inclusions of manganese oxide, which causes the arborescent markings. Some fine specimens come from the U.S.A., especially from Montana and Wyoming, and Nova Scotia also produces some interesting material. It is often difficult to believe that real vegetation is not included in some specimens. Exact formations of mosses, lichens, and other plants may be often observed, and some naturalists in the past have considered these dendrites as true cryptogamous plants.
Different names are given to agate according to the color of the bands. Black and white banded material is called onyx; the brown and white is sardonyx, and the red and white is known as red agate or carnelian agate. The beauty of these stones naturally depends upon the contrasting colors and degree of transparency of the bands.
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