Stilpnomelane is a very rare mineral at Franklin. This specimen was found in 1995 on the Buckwheat Dump and appears to be in the so called “Buckwheat Dolomite”. That is not an environment for “stilpnomelane” as described in Dunn’s monograph, but, apart from the presence of Zn, the EDS scan (see the “Analysis”) appears to be a good match for stilpnomelane as defined by the IMA. The scan is not a good match for franklinphilite or lennilenapeite, which supposedly can look similar. (The presence of Zn does suggest lennilenapeite or franklinphilite, however there seems to be no Mn at all. Mn would be required for franklinphilite and expected for lennilenapeite. Also, in both lennilenapeite and franklinphilite, one expects Fe to be subordinate to Mg. Of course, this was just a qualitative EDS scan. If it turns out to be lennilenapeite , which I doubt, then rejoice!)

Note: Dunn distinguishes ferristilpnomelane and ferrostilpnomelane as distinct species. The IMA is apparently monotheistic – only stiplnomelane is a true mineral. Also according to Dunn, “ferrostilpnimelane” and lennilenapeite form a series, so possibly this specimen is an intermediate member of the series – but close to “ferrostilpnomelane”.

Stilpnomelane is a difficult mineral to photograph. In this specimen, it occurs as lustrous very dark brown to nearly black platy/foliated “rosettes”. To see the individual plates, one needs reflections. But the reflections are mostly all-or-nothing. Either there is no usable reflection, or it is specular and causes “blowouts” in photos. While there appear to be some edges, most crystals look irregular/raggedy. (If euhedral crystals of stilpnomelane exist, it doesn’t seem as if any of the posts on Mindat have successfully captured an image of such crystals.)

FOV in the first pair of photos is 4.8 x 3.7 mm, 6.6 x 4.2 mm in the second pair, and 4.4 x 6.6 mm in the fifth photo, which also shows some of the small dolomite crystals (stained by Fe oxides).

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