FMF - Friends of Minerals Forum, discussion and message board

[Tracy]

Does anyone have any information on how common, or uncommon, are specimens of mica pseudo after tourmaline? I recently saw 2 specimens, one from Maine (Noyes Mountain) and one from Minas Gerais, and as they are a new thing to me I was curious. In the case of the Minas Gerais piece, the tourmaline is only partially replaced and there were some portions of green elbaite remaining. There is a photo of a Maine pseudo on mindat, it's at:
https://www.mindat.org/photo-1849.html
(link normalized by Jordi)

but I didn't find any photos on mindat of such pseudos from Minas Gerais. Does anybody have any more info about them? Thanks...

Tracy

[Les Presmyk]

I have seen these pseudos from Brazil. They are not common but they do exist. There is even a locality in Arizona for muscovite after schorl crystals. Not as large or attractive as those from Brazil but certainly interesting for Arizona.

[Pete Modreski]

I've seen muscovite after tourmaline (schorl) from one or more of the pegmatites in Colorado, too--for sure from the Tourmaline Prospect pegmatite, Crystal Mountain pegmatite district, Larimer County, and I think also from at least one of the pegmatites in Fremont County, CO. Finding such pseudomorphs with intact terminations is difficult, though.

Another classic locality for tourmaline in Colorado, one of the few for elbaite in the state, is the Brown Derby pegmatite, Quartz Creek (Ohio City) district, Gunnison County; here, the typically pastel pink to green or yellow tourmaline is soft, waxy-looking, and mostly altered to micas: I'll quote from Minerals of Colorado, 1997, p. 495:
"Some elbaite from the Brown Derby pegmatite is partially or completely altered to soft, yellow to pale violet, waxy or micaceous pseudomorphs composed of muscovite or cookeite." Again, intact terminated crystals are rare.

Pete Modreski

[Jon Mommers]

Hi Tak,

I have seen mica replacing tourmaline from a couple of Australian locations: Harts Range in the Northern Territory and from the Flinders Ranges in South Australia. Also saw a purported quartz replacing tourmaline from the Flinders Ranges area.

Cheers

Jon

[mmauthner]

Mica group and/or clay group pseudomorphs after tourmaline (and spodumene) are somewhat common in the mines here in the Pala district. If you are interested, next time I have my camera, I'll get a shot of the tourmaline pseudos one still sees in the wall. Not heading up this weekend so in a couple weeks...

Cheers,
Mark

[mmauthner]

As well, I used to have a beautiful deep pink mica pseudo after what I believed to be tourmaline from the Harding pegmatite in New Mexico...it was a bit squarish in cross-section though. Unfortunately, no pic...

Cheers,
Mark

[Tracy]

Thanks to all responders. My overall sense is that these pseudos are not everyday occurrences, but out there all the same. Mark, would love to see a photo when you get the chance.

- Tracy