Labradorite.—A kind of feldspar, commonly showing a beautiful play of bluish-gray colors, and, hence, much used for ornamental purposes. The finest specimens come from Labrador.
Lapis-lazuli or lazuli.—A mineral of a fine azure-blue color, usually occurring in small rounded masses. It is essentially a silicate of alumina, lime, and soda, with some sodium sulphide. It is often marked by yellow spots or veins of sulphide of iron, and is much valued for ornamental work.
Moonstone.—A nearly pellucid variety of feldspar, showing pearly or opaline reflections from within.
The best specimens come from Ceylon. Their value is not much more than the expense of cutting.
Obsidian.—A kind of glass produced by volcanoes. It is usually of a black color and opaque, except in thin splinters.
Onyx.—Chalcedony in parallel layers of different shades of color. It is used for making cameos, the figure being cut in one layer with the next layer as a background (see [cameo]). It is stained black and used to make mourning jewelry.
Opal.—A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity. The precious opal shows a peculiar play of colors of delicate tints and it is highly esteemed as a gem. One kind, with a varied play of colors in a reddish ground, is called harlequin opal. The fire opal (which comes from Mexico) has colors like the red and yellow of flame. This is not the cheap variety commonly called Mexican opal.
CELEBRATED HISTORIC DIAMONDS OF THE WORLD
