Idocrase. A mineral occurring in tetragonal crystals and also massive, of a brown to green color, rarely sulphur yellow or blue. It is a silicate of alumina and lime, with some iron and magnesia. It is common at Mt. Vesuvius.

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“Not a drop of rain falls in the sandy desert or on the barren rock, however useless it may seem to be, that is not seen to be of value by God, and that is not designated to accomplish some important purpose there.”
–Albert Barnes, Notes, Job 38:26