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[Peter Megaw]

Over the last 35 years distinctive fluorite-studded Celestine crystals have come out of the El Tule Mine area near Melchor Musquiz in Coahuila Mexico. I recently acquired a small lot and placed several in a display case with pieces I have had for some time. I was immediately struck by how similar most of the pieces are...and how different a few are. I suspect the sources are near neighbors rather than El Tule proper but do not know for sure. Nonetheless they sure make a nice group!

Here is a modified version of what I wrote for Rocks and Minerals recently

El Tule Mine, “Muzquiz,” Coahuila

El Tule Mine lies near Melchor Muzquiz, Coahuila, the town lying more or less at the center of a large regional cluster of low-temperature probable MVT fluorite deposits. Literally hundreds of small (1-8,000 ton), high-grade occurrences have been mined, many with specimen quality crystals, almost all of which are simply labeled “Muzquiz.” The deposits are relatively thin (2-5 meters thick) elongate bodies developed in limestone beneath a regionally extensive shale unit (Del Rio Shale). They are believed to be derived from formation brines (“connate waters”) expelled from the Sabinas and neighboring basins (Kessler 1977). Fluorites from throughout this region are readily recognized by abundant petroleum inclusions and the release of a strong fetid petroleum odor on trimming or scratching. This petroleum provides strong evidence for the involvement of basin brines in deposit formation. In many respects they resemble the fluorite deposits of the Illinois Fluorite District (Heyl 1982; Goldstein 1998; Lillie and Goldstein 2008) with fluorite replacing limestone and filling voids in collapse breccias developed during pre-mineral and intra-mineral cavern formation (Ohle 1985). They differ from the Illinois deposits in that they are closely associated with alkaline rhyolite intrusive bodies that may have contributed fluorine and acted as heat centers that helped focus mineralization (Kessler 1977). However, deep-seated intrusions are believed to underlie Hicks Dome, which hosts the Illinois Fluorite District (Heyl 1982), so the differences may be less than they appear.
Fluorite occurs in these Coahuila deposits with varying amounts of celestine and Baryte (often “celestoBaryte” or strontium-rich Baryte) and mining operations focus on the dominant mineral. Some are fluorite mines with byproduct (or contaminant) celestine/Baryte while others are celestine mines with associated fluorite. The eastern part of this region was the world’s principal producer of celestine for many years because strontium is an effective absorber of X-Rays, and it was a critical ingredient in reducing radiation from Cathode Ray color television screens and computer monitors. Unfortunately for collectors, LED and Plasma screen technology has superseded CRTs, so today most of the celestine operations are idle. Conversely, an upsurge in demand for fluorite has helped bring a number of the region’s fluorite dominant occurrences back into production with a resulting increase in availability of specimens.

Fluorites from El Tule and the general Muzquiz area are dominantly cubic, often with multiple elongate protuberances strongly resembling a cityscape. Crystals to 10+ cm are common, and color ranges from pale violet to purple to dark blackish-purple with the darker color reflecting a higher volume of petroleum-rich inclusions. Color zoning is often strong, generally with the darkest zones near the surface of the crystals. Perhaps the most distinctive specimens from El Tule are the large pale blue celestine blades studded with violet fluorite cubes. In rare cases the fluorite forms an almost complete jacket surrounding the celestine; an excellent example of this is found in the Houston Museum of Natural Science. Calcite is a common associated species but is commonly damaged and removed.

[Ru Smith]

Very attractive specimens, Peter. The hydrocarbon inclusions are interesting. Do you know what the thermal maturity of the local organic-rich mudrocks (Eagle Ford) is? Perhaps the source of the inclusions is local.

[Mark Ost]

Thanks for sharing those Pete. They are lovely specimens.

[gemlover]

those are fantastic looking specimens. thank you,

john

[Carlos M.]

Hi Peter:
That's an excellent display of fluorites.
Thanks for sharing more photos of your great collection.

[Herman van Dennebroek]

Very nice specimens Peter; and interesting information.

[Peter Megaw]

[Nico78]

I'm young and just start collecting since 15 years,
but I have never seen fluorite from this locality and of this quality!
The association with the celestite is simpling awesome!
So, a big thx for shared that!

And especially I really appreciate the fact that you explain and give some indications about the field and the geological context. It's much more interesting that some french forum where only pictures are posted...
Carry on :)