According to Mindat, mineral F (of Dunn) – aka UM1986-10 ClHMgMnZn to the IMA – is a valid but unnamed mineral. (According to Dunn himself, “It is assuredly a new mineral, only its definition is unclear”.) This particular specimen, along with several others, was found on the Sterling Hill Mine Run Dump in 1993, soon after the material was brought up from the mine by Museum staff. (The mine closed in 1986, and is now flooded up to essentially ground level). Material from this find has been analyzed via EDS (see the second “photo”).

In the first photo, (FOV 6.4 x 4.2 mm) mineral F is the pale cream “filling” in the “layer cake”. I’m not sure what the thin dark layers in the “cake” are. (They look similar to the heaterolite exsolutions commonly seen along zincite parting planes. But relating this stuff to zincite would be a geochemical stretch to say the least!) In places, instead of mineral F, the “filling” in the cake consists of glassy fluoborite needles (XRD verified on other specimens – see the third “photo”).

Weight 0.3 oz. Single item shipping weight 3.0 oz (no case). Up to 4 oz, this could be combined with one or two other small items for the same postage . Probably not suitable for a padded envelope.