Ankerite

Ankerite was first reported from Tsumeb by Pinch and Wilson (1977) citing a personal communication from Ed Ruggiero concerning material in the Zweibel Collection. They described ankerite as occurring "… on only a few specimens as drusy coatings of cream-colored crystals with calcite". Ankerite is also listed by Lombaard et al. (1986) as a rare and sparsely distributed mineral. Gebhard (1999) noted simply that ankerite occurs rarely as "… small tan crystals".

The term ‘ankerite’ has been used by sedimentologists and petrologists to describe minerals of the dolomite group containing in excess of 20 mol % Fe. The modern, IMA-approved mineralogical definition of ankerite, however, requires that divalent iron is the dominant cation in the Fe²⁺/Mg/Mn²⁺ - containing [MO₆] layer of the (dolomite group) mineral structure (Bridges et al. 2014). No analysis of Tsumeb ‘ankerite’ has been published, so it is possible that Tsumeb ‘ankerite’ could lie outside of the compositional field of ankerite sensu stricto, and that it may be correctly described as iron-bearing, or iron-rich dolomite.

Questionable status is retained for ankerite at Tsumeb pending analytical confirmation.