bayldonite after anglesite (?) (w. azurite)

TSNB731
Specimen
Holden, A.F.
Exhibit 1. Bayldonite after anglesite (?) (w. azurite); 115 mm.
Exhibit 1. Bayldonite after anglesite (?) (w. azurite); 115 mm.
Image Credit: Malcolm Southwood
Exhibit 2. 35 mm field of view.
Exhibit 2. 35 mm field of view.
Image Credit: Malcolm Southwood
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Specimen Title

bayldonite after anglesite (?) (w. azurite)

Associated Minerals

azurite

Principal Mineral

Bayldonite

Precursor Mineral (Uncertain)

Anglesite

Size

Cabinet; 115mm

Location in the Mine

First oxidation zone

Provenance

Holden, A.F.

Collection

MGMH; 109777

Entry Number

Specimen; TSNB731

Description

Elongated crystals of transparent, intensely blue azurite are a highlight of this specimen, but they rest on pseudomorphs of bayldonite (XRD verified) after anglesite (?) which is a rarely encountered combination at Tsumeb. The bayldonite replaces (or encrusts) elongate tabular crystals with arrowhead terminations (Exhibit 2); on one of these crystals the encrustation is incomplete, revealing a colourless, glassy interior (thereby precluding azurite as a possible precursor). The colourless mineral has not been analysed, but it is almost certainly anglesite (?), an observation consistent with the specimen’s high density.


The specimen is from the A. F. Holden Collection which was bequeathed to Harvard University in 1913. It is therefore unequivocally from the upper part of the first oxidation zone (i.e. 6 Level or above).