Tom, I think it’s likely that you are correct about the specimen being rockbridgeite (I don’t have a dog in this hunt). However, I don’t see that the two references you’ve cited necessarily prove that only rockbridgeite is found at Fletcher Quarry. The American Mineralogist article says that two specimens were analyzed from Fletcher Quarry and they were in the middle of the frondelite-rockbridgeite series (with Fe:Mn about 3:2, which makes them manganoan rockbridgeite). So yes, rockbridgeite has been found, and other specimens from there are likely to be rockbridgeite. But, are those two analyses enough to rule out frondelite? The Dana reference (Palache, et al) says “Frondelite occurs at Sapucaia….and a ferroan variety occurs at Fletcher Mine”. Perhaps specimens from Fletcher Mine should just be under the Frondelite-Rockbridgeite Series without specific, or more, analyses.

Hi Kelly,

Your thoughts are appreciated. I agree that an analysis of one or two specimens from a locality does not discredit the possibility that another, closely associated, species is present as well. However, I feel it is incumbent on the photo poster to "show cause" why a particular specimen ID is valid when there is no literature reference to support the claim. This is particularly true in this case where mangoan rockbridgeite and frondelite are visually identical AND even a quantitative EDS analysis cannot differentiate between the two species.

These fine distinctions are important to regional species collectors such as myself (New Hampshire).

Tom

Point taken. Interestingly, the most current version of Dana's Handbook ( Frondelite - Online Dana Handbook) show the Fletcher Mine as a locality for frondelite, although the references given provide little support. Good luck.

Hello everybody,


This piece came to me from a collection on the east coast (the former owner is now deceased so I can't him about it) and I simply copied down the label information. The piece subsequently has been sold, but I'm happy to change the listing, as I'm no expert on the Fletcher Mine.