Andyrobertsite

TSNB11
Mineral
First oxidation zoneThird oxidation zoneSupergene
Andyrobertsite: Platy electric-blue crystals comprising lamellar intergrowths of andyrobertsite and calcioandyrobertsite, associated with green zincolivenite. 35 mm field of view. Private Collection.
Andyrobertsite: Platy electric-blue crystals comprising lamellar intergrowths of andyrobertsite and calcioandyrobertsite, associated with green zincolivenite. 35 mm field of view. Private Collection.
Image Credit: John Schneider

Mineral Species

Andyrobertsite

Type Locality

Yes

Composition

KCdCu5(AsO4)4[As(OH)2O2] ∙2H2O1

Crystal System

Monoclinic

Status at Tsumeb

Confirmed (type locality)

Abundance

Extremely rare

Distribution

First and third oxidation zones

Paragenesis

Supergene

Entry Number

Species; TSNB11

Type Mineralogy

The type specimen for andyrobertsite (and calcioandyrobertsite) is believed to have been mined at Tsumeb in the early 1950s (Cooper et al. 1999), indicating a high probability that it is from the first oxidation zone. It originally belonged to Richard Baughart, a mining engineer working at Tsumeb but changed hands several times before being purchased by Bill Pinch at the 1996 Denver show, labelled as zinc-deficient keyite. Analysis demonstrated the presence of two new minerals, andyrobertsite (IMA 1997-022) and calcioandyrobertsite (IMA 1997-023). The crystal structure (of both minerals) was refined and solved by Cooper and Hawthorne (2000). Andyroberstsite was named to honour Andrew C. Roberts (b. 1950), mineralogist with the Geological Survey of Canada (Cooper et al. 1999). Type material is conserved at the Royal Ontario Museum (catalogue numbers M47022 and M47110) and at the Smithsonian Institution (catalogue number NMNH 171487).

General Notes

The type assemblage comprises andyrobertsite (with calcioandyrobertsite) on tennantite, with zincolivenite, and olivenite (Cooper et al. 1999). On the type specimen andyrobertsite and calcioandyrobertsite occur as intimate lamellar intergrowths that are crystallographically continuous and the two species are not visually distinguishable.

On the type specimen the intergrown minerals form platy crystals and are electric-blue in colour, with a vitreous lustre. The minerals are brittle with a good cleavage on (001) and a conchoidal fracture.

Associated Minerals

bradaczekite (?); calcioandyrobertsite; olivenite; tennantite-(Zn); zincolivenite