Olivenite

Olivenite


Composition: Cu2+2(AsO4)(OH)
Crystal System : Monoclinic
Colours: Olive-green, greenish-brown, grey, white
Lustre : Adamantine, vitreous
Hardness (H) : 3
Specific Gravity (S.G) : 4.38
References:

Bartelke (1976)

  

Distribution

Common. Occurs in all three oxidation zones, although end-member olivenite is relatively uncommon.

Occurrence

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

Notable Finds

Spectacular examples of acicular olivenite on a matrix of malachite and copper arseantes were found in the outcrop and the upper levels of the first oxidation zone (ref. Klein collection # 1050; Harvard University # 106045). Klein (1938) made the observation that olivenite was common between surface and a depth of 100 m, typically associated with azurite and malachite. In this part of the mine, olivenite occurred mainly as radial masses, sometimes with drusy surfaces of crystal terminations. Gebhard (1999) noted blocky crystals of olivenite to 50 mm but did not specify where in the mine they were found. However, Bartelke (1976) comments that blackish-green iron-rich olivenite was common in the second oxidation zone. (See also the notes on zincolivenite and adamite.)

Paragenetic and General Notes

Olivenite is the copper-rich end-member of the adamite-olivenite solid solution series and is defined as having a zinc:copper ratio of less than 25:75. At Tsumeb, olivenite (in the strict sense) is considerably less common than intermediate members of the olivenite-adamite series. Informally, the latter are referred to as "cuproadamite", although a probable majority of "cuproadamites", strictly speaking, belong to the recently defined species zincolivenite (Chukanov et al., 2007), defined as having a Zn:Cu ratio of less than 75:25, but greater than 25:75.

Some of Tsumeb's very rare and extremely rare arsenates occur in association with zincolivenite / "cuproadamite". The list of associated minerals provided is generic for the adamite-zincolivenite-olivenite series.

Minerals of the adamite-olivenite series (including zincolivenite) were considered by Keller (1977) to belong to "Type II" parageneses (i.e. mineral sequences forming at lower pH ranges). Zinc-rich members of the adamite-olivenite series were reported to have a wider range of associated secondary minerals than copper-rich members (Keller, op.cit.). Keller noted the following parageneses:

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

(2) primary sulphides >> conichalcite >> adamite >> schultenite (or chudobaite)

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

(4) primary sulphides >> conichalcite >> tsumcorite >> adamite >> smithsonite.

Olivenite is reported to form pseudomorphs after the following minerals:  bayldonite (rare).

The following minerals are reported to form pseudomorphs after olivenite:  adamite (rare, possible confusion with zoned crystals).