FMF - Friends of Minerals Forum, discussion and message board

[Jean Sendero]

Mexico is always producing fine minerals and lately it has proven again to be true.

First from Mapimi, around 2 months ago, some incredibly yellow to orange colored mimetite have surfaced that can rival San Pedro Corralito for the color. These have an inverted tear drop shape. Individual drops can reach 2 cm according to what I have seen. I was told that only 7-8 flats of the yellow mimetite surfaced of which only 2 had some cabinet and larger miniature sized specimens that were damaged free. The remaining flats were made of miniature size specimens that had suffered a lot of damage. Other shapes are observed which can be popcorn kernels-like.... For those that were at the Houston show, you probably had the chance to see a few of these yellow mimetite very early on. But, I was told that they sold almost instantaneously.

Santa Eulalia has produced hemimorphite for ever. In recent months however, instead of the more common elongated white crystals, some thick flat blades forming rosettes have emerged. These can be clear to almost 5 cm (individual crystal) with some goethite inclusions and or hematitic inclusions giving them a reddish color. The luster is simply stunning.

Additionally, some fantastic smithsonite pseudomorphing calcite have made it to the surface. The best ones have scaleohedron to 5 cm and are yellow. Yes, yellow. Most of the material is on the brownish side but very few have the yellow color. Unfortunately, the fast majority have damaged points. Undamaged specimens are rare.

I am certain that these will be seen during the summer shows.

Cheers

Jean

[Tobi]

Very interesting, Jean, thank you!

[Peter Megaw]

I have seen most of what Jean has mentioned here...although I still am looking for a mimetite as nice as his!

Jean is right that very few of the smithsonite pseudomorphs are undamaged and even fewer have great color like his...and the one below. Despite this three or four remain some of the best pseudos of this kind ever to emerge. They show successive replacement shells showing that the calcite was partially replaced, some was dissolved and the next layer was attacked. I have put several in acid and the internal structure shows that the smithsonite protrudes into the calcite...they are not simple epimorphs although they may have begun that way.

Apparently there is some production beginning from the top levels (8-9) of the Main Silicate Orebody in the Potosi Mine. This body is the.source of rhodochrosite and friends. The production stems from a Joint Venture between Grupo Mexico (owners of the Buena Tierra Mine and operators of the JV) and Minerales Nacionales de Mexico aka MINAMEX who own the Potosi Mine. This has reopened access to a lot of the upper level workings of the West Camp over the last 2 years, and we have already seen some benefits in the form of some large botryoidal smithsonites that came out in 2011 and 2012.

The hemimorphites that are coming out all come from the Oxide Zinc Orebody that extends from the 13th to the 17th Levels of the Potosi Mine. Some of the pieces have come out with brilliant black chalcophanite perched on the hemimorphite...and a few very nice willemites have also appeared.

On top of that are some nice and sharp triangular calcites from somewhere in the northern West Camp...probably the old Parcionera Mine (aka Goat Cave or Cueva de Chivas) another one of the major collctor access points for the West Camp.

Milpillas continues its decline. A few nice azurites have come out from under beds, but no decent material in any quantity has emerged. There have been a few oddly shaped malachite blobs...on and off matrix and a few large Barytes (to 5 cm) with a nice pale green-blue color. The cuprites that were available at Tucson time have disappeared.

[Pierre Joubert]

All Amazing specimens!!! Especially 2013 best hemi (8).JPG. Thank you Jean and Peter for showing.

[Carles Curto]

Why do you affirm smithsonite is pseudomorph after calcite if both minerals have the same crystalline forms? (and both are on the same group).
Is some calcite remaining into the crystals? or is it smithsonite recrystallized (perimorph) on previous smithsonite crystals? or are they simply smithsonite crystals?

[Roger Warin]

Hi
Thank you for sharing.
The crystalline texture may be favorable to pseudomorphosis, I think. Crystal size would be great for smithsonite.
Roger.

[Jordi Fabre]

The Mexican minerals are largely represented / discussed in FMF as it is easy to notice using the feature Mexico in FMF Gallery or searching the word "Mexico" in the Forum's search: .

For this reason and considering our luck to have here Jean Sendero and Peter Megaw, two great experts of Mexican minerals as well as many other Mexican collectors, I believe that this thread has a potentiality that does deserve to be in the Featured Columns of FMF section with the hope that in the future it could be a kind of window to new finds of Mexico were them appear grouped.

So, I renamed, numbered, and moved this topic to the Featured Columns of FMF section. For more info about how the Featured Columns of FMF section works, please use this link
Jean Sendero the author of the first post in this thread and therefore creator of it is already mentioned in the THANK-YOUs in the correspondent reference thread

[Peter Megaw]

Carlos asks a good question about why I call these pseudomorphs. As he suggests, first and most obvious (although not from the pictures) is that many have cores of remnant calcite. Second is that identical coarse scalenohedral calcite is the most common late vug lining mineral throughout the primary sulfide ores throughout the San Antonio Mine. At depth these are typically white semi-transparent crystals, often studded with pyrite. At depth in the pockets that produce ludlamite and vivianite the scalenohedral calcites are replaced by coarse siderite. Third these pseudomorphs occur at the modern...and ancient...watertable where zinc flushed out of the overlying oxidized sulfide mineralization (sphalerite-galena-pyrrhotite) is redeposited as a supergene blanket. This area contains caverns lined with ropy and stalactitic smithsonite, pockets lined with large botryoidal blue smithsonite and coarse rice-grain smithsonite crystals. No unquestionable "primary" scalenohedral smithsonite occurs in this area. Within the pseudomorph zone the pseudos range from nearly solid replacements on completely oxidized sulfides, to semi-solid replacements on untarnished sulfides. Sometimes there is remnant calcite, sometimes they are shells. These combined observations indicate pretty conclusively that these are not primary smithsonite crystals.

But are they true replacement pseudomorphs? Looking at the interior of either the natural shells or specimens where remnant calcite is removed by acid shows that the insides of the shells are irregular with numerous protrusions, not smooth as one would expect from an epimorph from which the substrate crystal was later dissolved. Further, in some cases the interiors show fins and boxworks of smithsonite with rhombohedral patterns suggesting infiltration and replacement by Zn-rich fluids along cleavage planes. In the latest examples there are multiple scalenohedral shells suggesting repeated attack of calcite surfaces by repeated batches of Zn-rich fluids.

I think the data indicate that these formed as Zn-rich, acid fluids derived from meteoric waters infiltrating through Zn-Pb-Fe sulfide ores reached the paleo watertable and were neutralized by contact with the typical scalenohedral calcite that occurs throughout the mine. With neutralization, smithsonite was deposited, perhaps/probably (?) usurping the carbonate from the calcite and kicking out the Ca to solution.

There is a more detailed explanation of this...with more pictures and figures in the Mineral Monographs "Smithsonite" issue published in 2012.

[Carles Curto]

[Jordi Fabre]

[Nico78]

The reddish Hemimorphite is pretty incredible!
Is it the real color, or is the picture a little different than the real one?
For several years I've been looking for a specimen, as was seen 5 years ago, of wulfenite in association with green mimetite from the Ojuela Mine.
Any news from this side? I was not able to buy a piece at that time, and now I still have some regrets as I can't find today a piece at a correct price...

In any case, a big thanks for sharing that with us!

[Peter Megaw]

Nico...the color is real

Yellow wulfenites on very yellow mimetite have come out of Ojuela recently. The best are VERY good...and very expensive.

There have also been more smithsonite pseudomorphs after calcite...but this time after bladed calcite instead of scahenohedral "dogtooth" crystals. The color is not as brilliant as the earlier ones, but the luster is very good. They also show a combination of epimorphic overgrowths and replacement pseudomorphing.

Bladed calcite is rare as "primary" calcite in the San Antonio Mine...most of the bladed calcite occurs in voids created during oxidation of the orebody, in contrast to the scalenohedral which is overwhelmingly associated with primary ore deposition. This just adds a nice fillip to the pseudomorphing story

Thanks to Ric for the shots

[Peter Megaw]

Got a chance to look through some more of the new Ojuela mimetites (with and without wulfenite) at Arkenstone during last weekend's Dallas Symposium...and picked up a few small pieces. Thought you all would enjoy the pictures...and encouragement to participate next year...the DMCS is growing quickly and is a lot of fun (if you avoid late-night sessions with TP and his Polish vodka!)

[Jean Sendero]

The classic localities, Mapimi, Santa Eulalia, Naica etc….all in the northern part of Mexico are producing specimens in quantity these days. A recent post by P Megaw on December 17 clearly shows this with the re-occurrence of the rhodocrosite from Santa Eulalia.

New localities are not commonly spoken of and even less common, new localities in the southern part of Mexico. A region that I am particularly interested in as it forms one of my main sub collecting interest of my Mexico collection.

This past October (Pacific NW chapter of the Friends of Mineralogy) and November (New Mexico Mineral Symposium), we have seen surfacing some new amethyst from these part of the country. The amethyst is not from the famous Amatitlan area or Las Vigas or Taxco but, it was originally thought to be from Zacualpan, in the state of Mexico north of Taxco. This is a small village where a few small silver mines are operating on a very small scale. The original pieces that made it to the market were few and rapidly found new homes in someone collection.

The amethyst form elegant groups with crystals that can reach 7 cm in length. They have a very dark purple core with the outer part of the crystals has a lighter color. The material shows good “gemminess”. The luster is moderate on most however some have great luster.

Since, XTAL – Dennis Beals Minerals, has been very busy acquiring more of these and has successfully done so. I have seen a variety of specimens ranging in sizes from miniature to simply giants. In the process of acquiring the lots from 3 different individuals, Dennis found out that the original locality thought to be Zacualpan was erroneous. It turns out to be in Guerrero but more than 75 km further to the east than the original locality.

This is a very exciting new find, a new locality in southern Mexico. I believe Dennis will have those out in Tucson with a serious new collection of tequila to sample.

[Tobi]

Wonderful specimens, thank you for sharing!