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Mineral F (of Dunn) & Fluoborite


Mineral F (of Dunn) & Fluoborite

Rare Mineral

Description Tabs

Sterling Mine, Ogdensburg, Sussex County, New Jersey, United States of America
Size Range: 
Miniature (4.5-7 cm)
3 × 6 × 5 cm

This is for collectors who enjoy stuff that isn’t just “pretty” and “straightforward”.

Mineral F (of Dunn) is an unnamed  mineral “officially” known as UM1986-10-CO:ClHMgMnZn. See Mindat MinIDs 04U-GY1 and PKC-DPS for links to discussions.  

Until recently, the Mindat species page for UM1986-10-CO:ClHMgMnZn stated that that it was unnamed but valid. It now states that it is “probably invalid”. But according to Pete Dunn (the original investigator), “It is assuredly a new mineral species; only its definition is unclear.” (“Franklin and Sterling Hill, New Jersey: the world’s most magnificent mineral deposits”, p. 689.)

Will it, or can it, ever be “defined” (according to current IMA standards)? I don’t know, but, as far as I can tell, mineralogists are not beating down the doors to get samples for whatever work needs to be done. Nonetheless, it is an interesting “thing”. Perhaps, as has been the case for several “UKs” from MSH (e.g. MSH UK 60 = arisite-(Ce)), it will eventually be found elsewhere in a form that permits complete characterization. Presumably the Sterling Mine would then be a co-type locality.

In this sample, Mineral F occurs with fluoborite (etc.) in a “layered blob” as a replacement for an unknown precursor. See Mindat MinID TG0-FQD for a discussion (and links to “more-than-you-wanted-to-know”) about this occurrence. Both the Mineral F and the fluoborite from this find have been analyzed. (See the “Analysis” tab or MinID TG0-FQD.)

The first pair of photos (FOV 6.8 x 3.9 mm) shows fairly typical cream colored “frothy” speheroids on fibrous/acicular fluoborite. The fluoborite could easily be taken for sussexite (or szaibelyite – which was the original supposition). But three different samples (with varying habits and sub-environments) from this find were analyzed (EDS, XRD) and they were all fluoborite.

The second pair of photos (FOV 4.6 x 6.8 mm) shows more of Mineral F and the fluoborite, but here Mineral F is not in well defined spheroids. The spheroidal habit is actually not common in the “blob” environment. Most of it is actually massive. But analysis shows that both habits have essentially the same chemistry.

In the second pair of photos the very dark red platy stuff may (or may not) be hetaerolite, but it has not been analyzed. Such platy hetaerolite is very common as exsolutions along parting planes in zincite. Furthermore zincite “blobs” (of similar size and shape), partly replaced by pyrochroite and carbonates were common in this find. However, it is very hard to see how a zincite “blob” with exsolved hetaerolite, could turn into a “layered blob” composed of fluoborite and Mineral F (while retaining the exsolved hetaerolite plates). Very strange but intriguing.

The matrix for this specimen is mostly red-fluorescent calcite with a bit of willemite. As can be seen from the SW UV photo, much of the willemite oc curs as a thin “rind” surrounding the blob. This is typical. In the blob itself, there is another, slightly pinkish carbonate that is not fluorescent and that does not fizz readily. It has not been analyzed. (The calcite “glows” more strongly on one side simply because that side was closer to the UV source. But this is not meant to be a fluorescent display specimen. Note also that this specimen is from the Sterling Hill Mining Museum Mine Run Dump, and has some weathered surfaces.)

Single item shipping weight (small box) is 6.2 oz. Up to a total weight of 8 oz (225 g), this could be combined with other items from this or future auctions for the same postage. If you wish to keep an “open box”, let me know. Please see my "Shipping Policy" for details.

Mineral Data
What's on the rock

Mineral F (of Dunn)

Synonym Of: 


Mg5(Zn,Mn)3(CO3)2(OH,Cl)12 · H2O
Mg5(Zn,Mn)3(CO3)2(OH,Cl)12 · H2O


Crystal System: 
Type Locality: 
Tallgruvan, Kallmora, Norberg, Västmanland, Sweden
Analysis Report - only: Mineral F (of Dunn) & Fluoborite
Analysis Report - only: Mineral F (of Dunn) & Fluoborite
LMB minerals

Seller Information

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Seller's terms and conditions

In addition to the standard terms and conditions, please note the following. Almost all IDs are visual. While in most cases the ID is obvious, there may be cases where it is not. If you are doubtful about a particular ID, please ask for more information. Or do not bid! Similarly, if you are not sure that the specimen meets your criteria, do not bid. I have tdone the best I can with the photos. Nevertheless, if you are not happy with a specimen for any reason, I will refund the bid price – but not the shipping costs (unless the fault is clearly mine) – if the specimen is returned. This policy applies even if analysis of the specimen shows that my ID was incorrect. When in doubt, ask - or don’t bid. Note that most crystals at MSH and Varennes are micros - even if on large specimens. Please pay attention to the stated sizes. Any customs duties, fees etc. are the responsibility of the buyer.