Malachite

Malachite


Composition: Cu2(CO3)(OH)2
Crystal System : Orthorhombic
Colours: Bright-green, emerald-green, dark-green, greenish-black
Lustre : Subadamantine, vitreous, dull, earthy
Hardness (H) : 3.5-4.0
Specific Gravity (S.G) : 4.05
References:

Bartelke (1976)

Distribution

Abundant. Occurs in all three oxidation zones, but especially common in the upper levels of the mine (first oxidation zone).

Occurrence

  • Supergene
  • 1st Oxidation Zone
  • 2nd Oxidation Zone
  • 3rd Oxidation Zone

Notable Finds

Crystals of non-pseudomorphous malachite to 10 mm were found in the first oxidation zone, as were very fine examples of malachite pseudomorphs after azurite. In the second oxidation zone, the so-called "Perkins Sams" azurite pocket also yielded very large and attractive malachite pseudomorphs. Large crystals of non-pseudomorphous malachite (with cuprite) were again found in the third oxidation zone (Gebhard, 1999).

Paragenetic and General Notes

Malachite is the most common secondary copper mineral at Tsumeb (Bartelke, 1976; Keller, 1977). Small acicular crystals of malachite, and aggregates thereof, are commonly associated with many other species.

A high proportion of the malachite specimen material from Tsumeb is pseudomorphous after azurite.

Malachite formed at several stages of the supergene process and is a constituent of a large number of diverse associations. It is generally an important component of Keller's (1977) "Type I" paragenesis (i.e. mineral sequences formed at higher pH ranges). Keller noted the following parageneses:

(1) duftite >> dundasite >> cerussite >> azurite >> malachite (ps. azurite).

(2) quartz >> mottramite >> olivenite >> duftite >> malachite >> azurite >> malachite (ps. azurite).

Malachite also occurs in the following Type II (i.e. lower pH) sequences:

(3) primary sulphides >> brochantite >> (posnjakite + malachite) >> linarite >> serpierite.

(4) primary sulphides >> conichalcite >> adamite >> azurite >> malachite

Malachite has been reported to form pseudomorphs after the following minerals:  aragonite (rare); azurite (abundant); copper (common); cuprite (common); enargite (rare); tennantite (rare); wulfenite (rare).

The following minerals have been reported to form pseudomorphs after malachite:  rosasite (common, the so-called "double pseudomorph", with the malachite itself pseudomorphous after azurite).