Stunning Malachite Crystals
Malachite is a famous and very popular semi-precious stone. It is named for the Greek word for "mallow", a green herb. Its banded light and dark green designs are one-of-a-kind, and give it a unique ornamental quality unlike that of any other stone. The light and dark green bands are so distinctive that malachite maybe one of the most easily recognized minerals by the general public. A popular design of ceramic ware which imitates this banding is named after the mineral malachite. It forms the banding from subtle changes in the oxidation states of the surrounding pore waters, but the exact mechanism is still not well understood.
Stunning Malachite Crystals From Sol Mine, Cerro de los Guardias, Rodalquilar, Níjar, Comarca Metropolitana de Almería, Almería, Andalusia, Spain |
Photo: Christian Rewitzer
Malachite is a green, very common secondary copper mineral with a widely variable habit. Typically it is found as crystalline aggregates or crusts, often banded in appearence, like agates. It is also often found as botryoidal clusters of radiating crystals, and as mammillary aggregates as well.
Malachite often results from the supergene weathering and oxidation of primary sulfidic copper ores, and is often found with azurite, goethite, and calcite. Except for its vibrant green color, the properties of malachite are similar to those of azurite and aggregates of the two minerals occur frequently. Malachite is more common than azurite and is typically associated with copper deposits around limestones, the source of the carbonate.
Malachite has a mineral impostor called pseudomalachite. Pseudomalachite is a copper phosphate that has a massive crystal habit and color that are very similar to malachite's habit and color, although the two minerals have different structures. Pseudomalachite means "false malachite" in latin and is very rare compared to malachite.
Color is banded light and dark green or (if crystalline), just dark green.
Luster is dull in massive forms and silky as crystals.
Transparency is opaque in massive form and translucent in crystalline forms.
Crystal System is monoclinic; 2/m.
Crystal Habit in its massive forms are botryoidal, stalactitic or globular. Crystals are acicular or fibrous and form in tufts and encrustations. Frequently found as pseudomorphs of azurite.
Cleavage is good in one direction but rarely seen.
Fracture is conchoidal to splintery.
Hardness is 3.5-4.
Specific Gravity is 3.9+ (slightly heavy).
Streak is green.
Other Characteristics: Weakly effervesces in acid.
Associated Minerals include limonite, chalcopyrite, bornite, native copper, calcite, cuprite, azurite, chrysocolla and many rare copper minerals such as kolwezite, shattuckite, antlerite, brochantite, graemite, aurichalcite, sphaerocobaltite, atacamite, chalcophyllite, conichalcite, rosasite, chalcosiderite, clinoclase, cornetite, duftite, libethenite, liroconite, mixite and mottramite among others.
Notable Occurrences include many classic mineral localities such as Shaba, Congo; Tsumeb, Nambia; Ural mountains, Russia; Mexico; several sites in Australia; England and several localities in the Southwestern United States especially in Arizona, USA.
Best Field Indicators are color banding, softness, associations and reaction to acid.