Malachite is Cu2CO3(OH)2 a copper carbonate mineral. It is usually found as botryoidal, fibrous, or stalagmitic masses. It crystallizes in the monoclinic crystal system; individual crystals, though rare, form as slender, acicular needles. The Greeks named malachite for its resemblance to the green color of the leaves of the mallow plant (molochitis).
Malachite typically forms as a result of the weathering of copper ore minerals, particularly around limestones (the source of the CO3 carbonate in the chemical formula). Malachite is referred to as a secondary mineral, because it forms when water containing CO2 or dissolved carbonate minerals seeps through copper ores (or vica versa). This is the same chemical reaction that causes copper flashing and copper ornaments exposed to the elements to turn green.
Malachite commonly occurs in massive form as tiny, fibrous, needle-like crystals aggregates. Malachite banding is caused by changes in the volume of groundwaters passing through the ore body as well as in their chemical composition. Banded specimens are often polished, or sliced and polished, to reveal their fabulous color patterns. When the bands form concentric rings it is called "bull's eye" malachite; specimens with this pattern are highly sought after. The light and dark green bands are so distinctive that malachite may be one of the mineral kingdom's most easily recognized minerals.
In massive form, malachite has a dull luster, and in crystals it has a silky, chatoyant shine. It is opaque when massive, though crystals can be translucent. Malachite crystallizes in the monoclinic system. When massive, malachite forms botryoidal (grape-like) balls, and also occurs as stalactites. Crystals of malachite are rare and usually small. They may be fibrous (as silky malachite) or acicular (as tufts and encrustations). Pseudomorphs after azurite are also common. Malachite has a hardness of 3.5 to 4, and a specific gravity of 3.9. Its streak is green, and is effervesces weakly in hydrochloric acid.
The main use for malachite is as an ore of copper, containing as much as 58% copper content. Malachite mining takes place on a huge scale, requiring the use of long drills, blasting, enormous loaders, and gigantic ore trucks.
Malachite is also used as an ornamental stone, for spheres, vases, and other decorative purposes. The most famous example is in Russia, where Czar Nicholas I created the famed Malachite Room in the Hermitage. This amazing chamber features room paneling and molding all carved out of precious malachite.
In jewelry, malachite is a very popular semi-precious stone. Banded malachite is frequently carved and polished into figurines, animals, plates, cups, and sculptural objects. It was formerly used as a pigment in green paints from ancient times until about 1800, when it began to be replaced by synthetic greens. It was also used in cosmetics, though this practice stopped when it was found that inhaling the dust was hazardous.
The majority of the world's malachite ore supply comes from The Democratic Republic of Congo (formerly Zaire), along with Namibia, Russia and the Southwestern U.S. For specimens, it has been found in classic mineral localities such as the Shaba Copper Belt in Katanga Province, D.R.Congo; Tsumeb, Namibia; Ural Mountains, Russia; Milpillas, Mexico; Arizona, USA; as well as sites in Israel, Australia, England and France.
FORMS OF MALACHITE FOR COLLECTORS
Mineral and gemstone collectors love malachite's many forms and habits, including botryoidal masses, stalactites (or slices cut from them), polished free forms, and spheres. Specimens with velvety, chatoyant fan and rosette formations made up of needle-like (acicular) crystals are especially highly prized. Another unusual habit is as fine acicular crusts and tufts, forming a mat of thin hairs like a carpet of green velvet. Here are examples of these many habits:
Silky malachite, also known as fibrous malachite or velvet malachite, is one the most unique, rare, and beautiful crystalline forms of malachite. Crystal needles are artfully displayed as radiating sprays which overlap and criss-cross each other, in gorgeous, chatoyant (shimmering) hues of dark to light green. The very fine aggregates of velvety malachite needles start from any number of centers on each surface. These needles (actually crystals) are typically ½" to ¾" long, but can reach lengths of up to several inches.
At the 2011 Tucson Gem and Mineral Show, several wholesale dealers offered a wide variety of impressive specimens of this unique form of malachite, from an exceptional find made during recent mining at the Mindingi Mine, Swambo, Katanga Province, D.R.Congo. This mine is a copper mine, worked from an open cut during the 1930's and 1940's without fully exploiting the deposit, and only recently reopened. The mine, located 5 km east of Swambo, is known for having yielded the first good specimens of cobaltocalcite during its early years. The quality of this new material was outstanding, and many specimens were made up entirely of extremely lustrous, shiny fans, bundles, sheaves, and rosettes of radiating crystal clusters.
Malachite stalactites form in large empty cavities created when malachite is dissolved by groundwater. Almost all have a small central channel, which may be the remains from an earlier, soda-straw stage. Stalactites are made up of radiating fibrous malachite with layers which vary in crystal size. Beware of fake stalactites, which are created by spraying powdered malachite mixed with glue onto plaster-coated metal wires or using similar processes. These fakes used to be common, but have, fortunately, disappeared in recent years. If it looks too good to be true, at a price that seems incredibly low for what it is, it is probably a fake.
Polished Malachite Stalactite Slices
Large, well-formed stalactites are sometimes set aside and sliced into thin slabs, which are then polished. The slices are usually around ¼" thick, and can be 6" or more in diameter. The slabs frequently reveal intricate bull's eye patterns made up of alternating light and dark band of malachite, making them objects of astonishing beauty.
Polished Massive Malachite
Due to its softness, malachite is easy to shape and polish. Free form pieces can range in size from a few inches to several feet. They are created by grinding a large piece into a flattened shape, then polishing the entire face. In other specimens, where there are deep channels in botryoidal malachite, the flat areas between the incised areas are polished to bring out the bull's eye patterns. This leaves the sides of the channels in their original state, which nicely complements the polished areas.
Polished Malachite Spheres
When large masses of malachite are mined, they can be fashioned into polished spheres. The process involves sawing the mass into a rough ball shape, then placing it in a machine with 2 or 3 circular grinding cups, followed by polishing cups with various grits, to give it a highly reflective polished surface. This is an extremely time consuming process, frequently taking 50 hours or more for medium size sphere.
Malachite is frequently found in botryoidal or mammillary specimens. A botryoidal mineral habit is characterized by a multiple hemispheres or a globular external form resembling a bunch of grapes. The term is derived from the Greek botruoeid?s, referring to a cluster of grapes. The size of the individual hemispheres can range from ¼" to several feet. Sometimes these globes are covered by secondary growths of malachite crystals, giving them a unique texture and sparkle.
Single crystals are very rare, though clusters of distinguishable crystals are sometimes found. In the specimen above, malachite crystals were formed atop a layer of black heterogenite, providing excellent contrast for the electric green malachite needles. Malachite crystals are typically acicular, but may be prismatic.
Malachite Pseudomorphs After Azurite
Malachite is frequently found as pseudomorphs after its sister, the mineral azurite. A pseudomorph is a crystal consisting of one mineral but having the form of another. Pseudomorphs are formed when the original mineral chemically replaces another mineral, but the outward appearance remains unchanged. The term comes form the Greek, where "pseudo" means false, and "morph" means shape. This transformation is intriguing, as it sometimes leaves a nearly perfect azurite crystal shape that is actually 100% malachite. Or, if the transformation is only partial, there is a mixture of both azurite and malachite in the altered crystals.
Malachite With Azurite
Aside from its vibrant green color, malachite's properties are very similar to those of azurite, so combinations of the two minerals are common. Specimens of bright green malachite with dark blue azurite make for one of the most dazzling color combinations in the mineral world.