rosasite after azurite (w. duftite after mimetite, and cerussite)

TSNB690
Specimen
Palache, C.
Exhibit 1. Rosasite after azurite (w. duftite after mimetite, and cerussite); 86 mm.
Exhibit 1. Rosasite after azurite (w. duftite after mimetite, and cerussite); 86 mm.
Image Credit: Malcolm Southwood
Exhibit 2. 30 mm field of view.
Exhibit 2. 30 mm field of view.
Image Credit: Malcolm Southwood
Exhibit 3. 50 mm field of view.
Exhibit 3. 50 mm field of view.
Image Credit: Malcolm Southwood
Exhibit 4. 25 mm field of view.
Exhibit 4. 25 mm field of view.
Image Credit: Malcolm Southwood
Exhibit 5. BSE image of zoned duftite after mimetite (Slovak Academy of Sciences, Bratislava, Slovakia).
Exhibit 5. BSE image of zoned duftite after mimetite (Slovak Academy of Sciences, Bratislava, Slovakia).
Image Credit: Martin Števko
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Specimen Title

rosasite after azurite (w. duftite after mimetite, and cerussite)

Associated Minerals

azurite; cerussite; duftite; malachite; mimetite; rosasite

Principal Mineral

Rosasite

Precursor Mineral

Azurite

Size

Cabinet; 86mm

Location in the Mine

First oxidation zone

Provenance

Palache, C.

Collection

MGMH; 87530

Entry Number

Specimen; TSNB690

Description

A pistachio-green matrix of massive, cryptocrystalline Cu and Pb arsenates supports a complex paragenesis of arsenate and carbonate minerals. Mimetite (prismatic to 4 mm) was the first well-crystallised species to form, but the crystals have been replaced to varying degrees by duftite (EDS confirmed. Martin Števko; Slovak Academy of Sciences, Bratislava, Slovakia). A first generation of azurite crystals (to 4 mm) formed next in the sequence, but was subsequently altered to malachite which, in turn has been partly replaced by blue-green rosasite (Raman verified; Exhibit 2). A second generation of azurite as prismatic crystals (to 6 mm) is essentially unaltered but is succeeded by colourless to slightly smoky cerussite crystals (to 5 mm).

The alteration of mimetite to duftite is particularly interesting (exhibits 3 and 4). In most cases the mimetite is completely replaced or dissolved away so that many of the replacements are hollow epimorphs. Electron microprobe analysis shows variation in the composition of the duftite (Exhibit 5) with the lighter bands consisting of near end-member duftite and the darker bands enriched in calcium.


The specimen is from the collection purchased by Charles Palache during his visit to Tsumeb in December 1922, which dates it to the upper part of the first oxidation zone (i.e. 8 Level or above).

Compare with specimen MGMH96988.