arsentsumebite after mimetite

TSNB783
Specimen
Palache, C.
Exhibit 1. Arsentsumebite after mimetite; 98 mm.
Exhibit 1. Arsentsumebite after mimetite; 98 mm.
Image Credit: Malcolm Southwood
Exhibit 2. 40 mm field of view.
Exhibit 2. 40 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

azurite; bayldonite; malachite

Principal Mineral

Arsentsumebite

Precursor Mineral

Mimetite

Size

Cabinet; 98mm

Location in the Mine

First oxidation zone; 4 Level

Provenance

Palache, C.

Collection

MGMH; 146313

Collected by

Charles Palache; 6 April 1922

Entry Number

Specimen; TSNB783

Description

A dense accumulation of green Cu/Pb arsenate minerals, slightly vuggy, with pseudomorphs of arsentsumebite (EDS verified) after mimetite (to 10 mm) in the vugs. Azurite has formed on the arsenate pseudomorphs as pristine crystals (exceptionally to 4 mm) but there are also sparse pseudomorphs of malachite after azurite in close juxtaposition.


Preliminary investigation by EDS shows the mimetite is replaced principally by arsentsumbite with only minor bayldonite (Martin Števko pers. comm.; Slovak Academy of Sciences, Bratislava, Slovakia). The replacement is extensive but incomplete; broken pseudomorphs reveal just a very little mimetite remaining in the cores of some of the structures.


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. The specimen is from the same occurrence as MGMH146311 and the two pieces share the same field number.