MSH is known for all sorts of weird and wonderful pseudomorphs. On this specimen, the mineral replaced was a member of the burbankite family, probably petersenite-(Ce).  Many types of PSM after petersenite-(Ce), some quite large, are known from the Poudrette pegmatite. The best know are probably the tan/brown replacements by micaceous synchysite-(Ce). According to quick and dirty EDS (see the “Analysis” tab), this is also synchysite-(Ce) (even the blue-green outer “rind”), but this cavernous, grainy/chalky type is less common.  Found 8/16/97.

The first pair of photos (FOV 4.3 x 6.8 mm) shows pretty much all of the pseudomorphs, the longest being about 4.3 mm. Some of them are crudely “terminated”. But the most interesting thing here is the blue-green color. Unfortunately. the only hint provided by the EDS scan is the presence of Th.

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