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. It is stained black and used to make mourning jewelry.

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“God is a skilful physician. He knows what is best. God observes the several tempers of men, and knows what will work most effectually. Some are of a more sweet disposition, and are drawn by mercy: others are more rugged and knotty pieces: these God deals with in a more forcible way. Some things are kept in sugar, some in brine. God doth not deal alike with all, he hath trials for the strong, and cordials for the weak.”
–Thomas Watson, A Divine Cordial