Arsentsumebite after mimetite

TSNB782
Specimen
Palache, C.
Exhibit 1. Bayldonite (?) after Mimetite; 73 mm.
Exhibit 1. Bayldonite (?) after Mimetite; 73 mm.
Image Credit: Malcolm Southwood
Exhibit 2. 25 mm field of view.
Exhibit 2. 25 mm field of view.
Image Credit: Malcolm Southwood
Exhibit 3. Specimen label (Shaler Memorial Expedition).
Exhibit 3. Specimen label (Shaler Memorial Expedition).
Image Credit: MGMH Archive
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Specimen Title

Arsentsumebite after mimetite

Associated Minerals

arsentsumebite; azurite; bayldonite; cerussite (?)

Principal Mineral

Arsentsumebite

Precursor Mineral

Mimetite

Size

Cabinet; 73mm

Location in the Mine

First oxidation zone; 4 Level

Provenance

Palache, C.

Collection

MGMH; 146311

Collected by

Charles Palache; 6 April 1922

Entry Number

Specimen; TSNB782

Description

A dense accumulation of green Cu/Pb arsenate minerals – probably a mixture of arsentsumebite (?) and bayldonite (?) with massive off-white cerussite (?). A vug on the display face hosts pseudomorphs of arsentsumebite (EDS verified) after mimetite with broken surfaces indicating a zoned replacement that is more or less complete; some of the replacement structures enclose a narrow hollow core.


Preliminary investigation by EDS of a specimen from the same occurrence (MGMH146313) shows the mimetite is replaced principally by arsentsumbite with only minor bayldonite (Martin Števko pers. comm.; Slovak Institute of Sciences, Bratislava, Slovakia).



Two pristine crystals of azurite (to 1.5 mm) on the pseudomorph surfaces complete the paragenesis (Exhibit 2).


This specimen was collected by Charles Palache of Harvard University, during an underground visit at Tsumeb at the time of the Shaler Memorial Expedition to South Africa. It carries a Shaler Expedition label (Exhibit 3) with a field number – 13930 – in addition to its MGMH catalogue number. Compare with MGMH146313.