Quiz: Remember the definition of mal de mer?
a silicate mineral, hydrated copper silicate, CuSiO32H2O, formed as a decomposition product of copper minerals in most copper mines, especially in arid regions. It occurs as crusts or masses in the upper parts of copper-ore veins where the copper minerals have been altered by water containing dissolved silica. Specimens with a fine green or bluish-green colour may be used as ornamental stones. For detailed physical properties, see silicate mineral (table)