fraipontite

Fraipontite is a member of the kaolinite-serpentinite group of minerals. It was first observed at Tsumeb by Medenbach et al. (1983b) as part of the type assemblage for gebhardite in association with hematite, mimetite, quartz, reinerite, smithsonite and willemite.

Keller and Bartelke (1982) and Keller (1984) noted that fraipontite also occurs in other parageneses with willemite and cerussite. It typically presents as aggregates of platy (or scaly) off-white to grey-white pearlescent crystals that could easily be confused with kaolinite, kegelite, phlogopite or hydrocerussite. Keller and Bartelke (1982) observed that fraipontite is very easily overlooked so that its abundance at Tsumeb may have been underestimated.

Lombaard et al. (1986) listed fraipontite as a "very rare" mineral at Tsumeb. Gebhard (1999) described fraipontite as "rare" and implied that it only occurs in the gebhardite paragenesis.

Fraipontite has been identified as part of an unusual paragenesis with a scheelite-powellite series mineral, siderite and quartz on massive sulphide ore (Mark Feinglos; pers. comm. to M. Southwood, September 2015; see also Southwood 2019). The specimen is now at Harvard University (MGMH 2022.4.10385L).

A specimen in the Pinch Collection (MGMH 2020.7.3321) consists of a shard of altered, iron-stained dolostone (?) encrusted by a layer of chalky-white fraipontite (EDS and XRD verified), apparently in part pseudomorphous after an unidentified precursor mineral. The fraipontite is in turn extensively overgrown by a lime-green crust comprising intergrown spherules (to 1 mm) of conichalcite.

cerussite; chalcocite; conichalcite; gebhardite; geminite; hematite; mimetite; powellite; quartz; reinerite; scheelite; schulenbergite; siderite; smithsonite; stolzite; willemite; zharchikhite