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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“When the soul is once taken up with the things that are of absolute necessity, it will not be much troubled about other things.”
–Jeremiah Burroughs, The Rare Jewel of Christian Contentment