FMF - Friends of Minerals Forum, discussion and message board

[GneissWare]

I bought an old collection about 15 years ago that seems to be from the 1940s to the 1960s in dates assembled, and I put away several specimens I found interesting.

It is labeled Mina La Majura, Mexico, which I can't find on Mindat. This specimen is probably mislabeled with a phonetic variant of its true locality.

I suspect it is from one of the following:
1. Matehuala, Sierra del Fraile, San Luis Potosí, Mexico
2. Mojina Mine, Mun. de Ahumada, Chihuahua, Mexico

The photos don't really do the piece justice. The celestine is very blue and seems to be intergrown with and perched on the calcite.

Just wondering if anyone remembers seeing this material coming out in the 1960s or earlier? Any help would be appreciated.

Bob

[Luis Domínguez]

I'm very sure that this specimen is from San Luis Potosí, probably from Sierra del Fraile.

greetings

[Peter Megaw]

Bob, Your second guess is very close. It is classic material from Mina Mojina, Ricardo Flores Magon, Municipio Buenaventura, Chihuahua, Mexico.

Your guess on the timing is good too. Benny Fenn brought out a LOT of these in the late 60s and sold most of them to Suzie Davis here in Tucson.

The Mojina Mine is a classic carbonate replacement deposit that lies about 2/3rds fo the way between Santa Eulalia and San Pedro Corralitos in north-central Chihuahua. It sits about 100km west of Villa Ahumada. Mojina produced high-grade oxide lead-silver-zinc ores with minor gold and tellurium from mantos located on the upper and lower contacts of a felsic sill. The mine intersected a series of caverns lined with calcite...most were the "popcorn" like growths like yours. Rarer were pockets lined with "cobra-calcite" ...well crystallized calcite with distinctive curved rhombs up to 3-4 cm across that look like upright cobras with their hoods spread. Some of these have sharp blue celestine crystals on them. I will endeavor to post a picture of mine tomorrow.

Never a big mine, it might have produced 100,000 tonnes. However, we are working to rectify that...as we are currently seeking the source of this nifty manto.

[GneissWare]

Peter,
Thanks for the great info on the deposit. I look forward to seeing the photo of your specimen.
Bob

[GneissWare]

[Peter Megaw]

Bob...The Sierra Mojina lies east of Flores Magon...more or les exactly between the symbols for highways 10 and 7. I have no problem with putting the photo on Mindat, but I am sure the rancher would prefer not to have the place too specifically located, he has had problems with expensive cattle getting loose when gawkers have gone up to the mine. He is definitely NOT disposed to let folks enter the mine.

I note a couple of interesting things on Mindat. First, they tie the mine to the Constitucion ejido rather than Flores Magon. Constitucion is marginally closer but is a pretty tiny community (<300 people) versus sevral thousand in Flores Magon. In Panczner's time the only access to the mine would have been through Constitucion, but the recent construction of Highway 7 changed that. Panczner and Mindat have the municipio wrong...it is Buenaventura, not Ahumada.

There is a photo of a cobra caclte on Mindat that sort of shows what I mean by the hoods

Another thing to note that you can see pretty clearly comparing the pictures...and your specimen, is that many of these were washed with hydrochloric acid to remove the outermost layer of fine-grained matte calcite and give them a glossy appearance. Some are naturally glossy however, so you need to look closely to see if acid was used. Even most of the best naturally glossy specimens will show patches of the matte calcite...the acid washed ones are uniformly glossy...and this often includes the point of attachment, which is glossy or with rounded edges is a dead giveaway of acid washing.

Unfortunately, acid washing remains a common practise of bulk commerical dealers.

[GneissWare]

Peter:
I think I fixed the Mindat locality to conform with your info. It is at https://www.mindat.org/loc-16461.html I also added in the info about the geology of the deposit to make sure this info which is really hard to find is also preserved. I hope this is OK--if not I can remove. I will also post your photo of the pocket, but not the mine to try to insulate the rancher.

Thanks again. You are a wealth of info!
Bob

[Jim Robison]

The following pics are all from Mina la Mojina and show the classic cobra head calcite. My piece does not have the single distinctive 'heads' like I expect Peter's will show. Rather, they are complex 'multi-headed' creatures. Still very interesting.

[Peter Megaw]

Nice specimen Jim! How big is it?

As promised here are some shots of my cobra calcites...with and without celestine.

[Jim Robison]

Peter

Lost my respons the first time. My piece is about 18 cm by 7 cm wide by 5 cm in height. The matrix is a spot on match with your piece, including I suspect the clay parting layer on the bottom.

Have to confess that this near-sighted collector had completely missed the small blue celestine crystals/blebs on my piece until I looked at your lovely specimen. Turns out there are at least a half-dozen there. I wonder why mine has the lumpy whitie overgrowths on the heads of the 'cobra's?"

[Peter Megaw]

If it wasn't so nice I'd think you got it from me? I bought a huge slab at the end of the Tucson Show about 4-5 years ago. It was a fin easily 40 by 60 cm and 8-15 m thick with cobra heads on both sides. Would have been a keeper as-was except for a big whanger right in the middle of the best view surface...why the delare let it go for a reasonable price. I had it carved into a dozen really nice pieces completely free of damage...and "dispersed" about half of them.

I'd guess they came from the same pocket if not the same part of the pocket.

[Jim Robison]

Peter

Not from you, although I would have loved to pick up one of the pieces from your big chunk of rock!

Got mine from Kristalle in 1988 when a worldwide carbonate collector (whose name escapes me at the moment) in the San Francisco Bay area was having Wayne and Donna disburse his collection Got a number of very fine pieces, and my only regret is that I didn't get a whole lot more.

I think you must be right about all coming from the same pocket. Too many similarities.

[Darren]

Peter, just wanted to say thanks. I am quite attracted to Mexican pieces, living here in southern New Mexico, and always enjoy the information you provide - not just "text," but photos, maps, etc. It really makes these threads about Mexican minerals a joy to peruse. Cheers!

Darren

[Peter Megaw]

Jim...what else did you get from Mexico?

Darren...where in southern NM...that's not far from here..

[Jim Robison]

Peter

Right at the moment I can't recall any other Mexican pieces. I got a nice group of European specimens, a Morro Velho piece, and some really nice English calcites.

What I passed on, because I wasn't in the hunt then, was a bunch of Tsumeb carbonates of all flavors, a small cab absolute killer cerussite twin/dioptase/wulfenite piece from Mammoth St. Anthony (good enough if I had it to put in that case next year), and several others. Ah well, we live and learn. That was when I learned that if you see it and can afford it (and maybe even if you can't), buy it now because you may never have another chance.

I have a lot of Mexican material. Someday I need to show you the collection when you are up in Phoenix. Right now I'm two days away from heading up to the Pacific NorthWest for a spell. We'll talk again in the fall. I still (always will) have the neon blue smithy from San Antonio Grande that I got from you maybe a decade or so back. One of my prized pieces.

Jim