duftite (w. calcite)

TSNB443

Specimen

Exhibit 1. Duftite (w. calcite); 80 mm.
Exhibit 1. Duftite (w. calcite); 80 mm.
Image Credit: Malcolm Southwood
Exhibit 2. 55 mm field of view.
Exhibit 2. 55 mm field of view.
Image Credit: Malcolm Southwood
Exhibit 3. Back-scattered electron image of a single duftite spherule. Analytical data for the traverse A-B is presented in Exhibit 5.
Exhibit 3. Back-scattered electron image of a single duftite spherule. Analytical data for the traverse A-B is presented in Exhibit 5.
Image Credit: Jeff Chen
Exhibit 4. Analytical data. Mean compositions for duftite (i) and duftite (ii); refer to specimen description. Both generations are calcium rich. (M. Southwood and P. Carr; unpublished).
Exhibit 4. Analytical data. Mean compositions for duftite (i) and duftite (ii); refer to specimen description. Both generations are calcium rich. (M. Southwood and P. Carr; unpublished).
Image Credit: Malcolm Southwood
Exhibit 5. Analytical data. Compositional variation of a duftite spherule. Analyses at 50 micron intervals along traverse A-B (see Exhibit 3).
Exhibit 5. Analytical data. Compositional variation of a duftite spherule. Analyses at 50 micron intervals along traverse A-B (see Exhibit 3).
Image Credit: Malcolm Southwood
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Title

duftite (w. calcite)

Principal Mineral

Duftite

Size

Cabinet; 80mm

Collection

Southwood, M. MS2012.029

Provenance

Bahmann, U.; Bruce, I.

Entry Type

Specimen TSNB443

Description

Spheroidal aggregates of lustrous, dark-green duftite (to 1 mm), singly, and as clusters on calcite and minor dolomite (?), the latter as isolated single crystals and small intergrowths of colourless, twisted rhombs. The calcite is tan coloured presumably due to iron staining and, under magnification, inclusions of iron oxides (?) are visible in some crystals.

Close examination shows two generations of duftite (Exhibit 2); the darker green spheroids are duftite (i) for which SEM study shows an intricate concentric zoning (Exhibit 3); duftite (ii) consists of lime green individuals and aggregates on exposed calcite and on duftite (i).

The crystallisation sequence appears to be: calcite >> duftite(i) >> dolomite >> duftite(ii).

Quantitative WDS analysis (Exhibit 4) shows both duftite generations are Ca-rich, but that (i) has a slightly higher Pb/(Pb+Ca) (=0.65) than duftite(ii) (=0.63). Neither generation contains appreciable zinc; Cu/(Cu+Zn) ranges from 0.97 to 0.98.

Exhibit 5 shows the compositional variation within one of the duftite (1) spherules.

The specimen was formerly in the collection of Uli Bahmann (South Africa) and was purchased by its current owner from Ian Bruce (Crystal Classics).

Associated Minerals

calcite; dolomite (?); dolomite