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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“Prayer and thanks are like the double motion of the lungs, the air that is sucked in by prayer is breathed forth again by thanks.”
–Thomas Goodwin, The Return of Prayers