Title
plancheite
Composition
Cu8(Si4O11)2(OH)4·H2O
Crystal System
Orthorhombic
Status at Tsumeb
Confirmed
Abundance
Somewhat rare
Distribution
Second oxidation zone.
Paragenesis
Supergene.
Type Locality
No
Entry Type
Species TSNB279
General Notes
The earliest published mention of plancheite at Tsumeb is by Geier (1973/1974) who observed that on and below 30 Level, dioptase and the chemically related mineral plancheite "… gained a certain importance as not-so-rare minerals".
Bartelke (1976) commented that plancheite usually occurs as dense, light blue masses and powder-like surface coatings but that more rarely, it forms radiating spherulites (to 1 or 2 mm) in small cavities.
According to Pinch and Wilson (1977) plancheite of the spherulitic habit was sometimes mis-identified as bisbeeite (a discredited silicate of copper and magnesium; www.mindat.org; accessed February 2023).
Keller (1977a) placed plancheite in one of the subdivisions of his "Type I" paragenetic sequences (i.e., sequences forming at relatively high pH values) as follows:
I/9: dolomite >> duftite >> plancheite >> dioptase(i) >> calcite >> dioptase(ii)
Gebhard (1999) cautioned that "… chrysocolla, plancheite and shattuckite all somewhat resemble each other … they have been found sparingly throughout the deposit." He also observed that "Pseudomorphs of plancheite after azurite are famous, but rare from Tsumeb."
Associated Minerals
aragonite; azurite; calcite; cerussite; conichalcite; dioptase; dolomite; duftite; fornacite (?); malachite; willemite; wulfenite
Pseudomorphs
Plancheite has been reported to form pseudomorphs after the following minerals: azurite (rare), cuprite (rare).
