Marecottite is a rare mineral that typically occurs as a secondary mineral in copper and lead deposits. It is a complex hydrated copper chloride hydroxide, with the chemical formula Cu2(AsO4)(OH)3•3H2O. The mineral is named after the location of its discovery - Marecottes, Switzerland.
Marecottite forms small, prismatic crystals that are often aggregated into crusts or botryoidal masses. It exhibits a bright turquoise or greenish-blue color, which is highly distinctive and visually appealing. The mineral possesses a vitreous to pearly luster and a transparent to translucent appearance. Its streak is light blue.
In terms of physical properties, marecottite is relatively soft, with a Mohs hardness of around 2. It has perfect cleavage along one direction, which can be seen on the crystal faces. The mineral is not highly dense and typically has a specific gravity between 3.15 and 3.20.
Marecottite is primarily found in oxidized copper and lead deposits that have undergone weathering, where it forms as a result of chemical reactions between hydrothermal fluids and the surrounding rocks. It is usually associated with other secondary copper minerals like malachite, chrysocolla, and azurite.
While marecottite is not a widely recognized or commercially important mineral, it is valued among mineral collectors for its unique color and crystal habit. Due to its scarcity, specimens of marecottite are relatively hard to obtain, and they are usually sought after by collectors of rare and exotic minerals.
