The main photo (FOV 5.9 x 4.2 mm) shows fluoborite needles to about 1¼ mm. Most of the specimen is shot through with such needles.

Fluoborite is not uncommon at Sterling Hill and can come in much larger, fibrous, aggregates which can look very similar to sussexite. But the glassy needles from this find have been XRD verified on three other specimens. (The habits varied, but all three were found to be fluoborite.)

This specimen is from an interesting find, in which the fluoborite is often associated with Mineral F (of Dunn), aka UM1986-10-CO:ClHMgMnZn). There is no Mineral F on this sample (but the brown spheroids scattered about may be what is left of it in this case.)

Note the diagonal black lines which appear to divide the fluoborite into layers. These are actually very thin sheets of what may be hetaerolite. Thin exsolution sheets of heatarolite often divide Sterlinh Hill zincite into similarly spaced layers. And it seems likely that the layered structure here is relict from some precursor. However, it boggles the mind to think of how fluoborite could replace zincite! The origin of this material is a very curious puzzle.

Weight 0.4 oz.