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 is highly esteemed as a gem. One kind, with a varied play of color in a reddish ground, is called harlequin opal. The fire opal (which comes from Mexico) has colors like the red and yellow of flame.

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“Let us urge forward our spirits, and make them approach the invisible world, and fix our mind upon immaterial things, till we clearly perceive that these are no dreams; nay, that all things are dreams and shadows besides them.”
–Henry Scougal, The Life of God in the Soul of Man