Adamite

Adamite


Composition: Zn2(AsO4)(OH)
Crystal System : Orthorhombic
Colours: Colourless, white, pale-yellow, yellow, green, plum
Lustre : Vitreous. Sub-vitreous, waxy, greasy
Hardness (H) : 3.5
Specific Gravity (S.G) : 4.32-4.48
References:

Bartelke (1976)

Distribution

Rare. Although the adamite-olivenite series is well-represented in all three oxidation zones, end-member adamite is very much subordinate in abundance to intermediate members of the series (see zincolivenite).

Occurrence

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

Notable Finds

The occurrence of cobaltian adamite in the first oxidation zone is notable (see Karabacek collection # 4318, Harvard University # 93828). In the third oxidation zone, very unusual white, needle-like crystals of adamite occurred with leiteite and legrandite in the "Zinc Pocket", on 44 Level. (See also the notes on zincolivenite, and olivenite.)

Paragenetic and General Notes

Adamite is the zinc-rich end-member of the adamite-olivenite solid solution series and is defined as having a zinc:copper ratio exceeding 75:25. At Tsumeb, end-member adamite is relatively rare, although crystals to 37 mm (on smithsonite) have been reported (Von Bezing et al., 2014). On the other hand, adamite with some degree of copper substitution (informally referred to as "cuproadamite") is widespread at Tsumeb. It occurs in cavities in tennantite-rich massive sulphide as the only secondary mineral, but also in a number of different parageneses comprising a wide range of secondary minerals. A probable majority of "cuproadamites", strictly speaking, belong to the more 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 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.

Adamite has been reported to form pseudomorphs after olivenite (rare; Gebhard, 1999).