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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“And we know that in all things God works for the good of those who love him, who have been called according to his purpose.”
– Romans 8:28