Malachite Blue (Lazulite)
Lazulite and malachite (mountain blue) are of frequent occurrence in copper mines, and the former is distinguished by its beautiful azure blue colour, which, however, suffers considerably when the crystals are reduced to powder. Both minerals are very similar in chemical composition, and consist of cupric carbonate. The formula of malachite is 2CuOCO2 + H2O, that of lazulite being 3CuO(CO2)2 + H2O, so that the only difference between them is that of the relative proportions of the substances in combination. Lazulite is also rather hard (3·5–4·0), but owing to the small size and brittle character of the crystals it is not very difficult to pulverise. In the air, malachite blue behaves in much the same way as malachite green, turning black in presence of sulphuretted hydrogen.
Malachite blue is chiefly used for indoor work, and also as a water colour; but it is always rather pale and dull.