Jeff Davis County, Texas road cuts

Hi, all!

I obtained an egg carton of material from the giveaway table at the 2012 Rochester Symposium's Micromounter's Playroom. The locality is given as "Route 166 Roadcut, 35-40 miles south of Kent, Jeff Davis County, Texas". Minerals listed include cryptomelane, tridymite, opal and chalcedony. I see blue-black needles and mats, golden spherical crystal aggregates (goethite?) and many other minerals that will get further examination when I get back from Rochester. I'll also post pictures. The matrix is a red-brown hard stone, not crumbly like limonite. The chalcedony and opal coatings in the vugs are pale blue to violet in color. Haven't checked for fluorescence yet.

Mindat does not have this locality in the database. Anyone familiar with the area, the locality or the minerals foumd there? Any references such as local club field trip reports?

Thanks!

Steve Stuart

Lot of basalt (and rhyolites) in the area. I'd probably refer to it as west of Fort Davis.

I see your point about the roadcut(s) being closer to Fort Davis than Kent. Here are some images.


Possibly notronite or similiar species


The fine black acicular species (cryptomelane or something else)


Possibly tridymite coated with opal or chalcedony

Anyone else want to chime in?

Steve

That area is many miles of nothing but hills, rocks, jack rabbits, rattlesnakes, a few cows and some humans. Plenty of mineralization, abundant agate - Much private land, lots of posted No tresspassing. Best starting point would Art Smith's 1991 Rocks & Minerals article on the Minerals of Texas (vol. 66 no. 3). Art was a great micromount person - and the EXPERT for Texas minerals. A huge amount of Texas knowledge was lost with the passing of my friends Art, and Dr. Al Kidwell. I have a ton of Texas information, however, currently packed in boxes after a recent change of location. Will see what more I can find. ....Hal Prior

Don't have that issue in my library.

I think that I posted all of Art's locality info from the article here on mindat. Art donated a lot of his personal library to the Houston club (where he was librarian). I am not sure how much of his info was input into the computer that was used by the library.

Some possibilities:

[www.mindat.org]

The locality photo shows the red-pink-brown color of the matrix rock that my specimens have. My locality is probably similar, but the information I have specifies Rte 166, not Rte 118.

[www.mindat.org]

16 miles west of Fort Davis off Rte 166. Has opal, which is one of the minerals listed on my egg carton.

The micros are really interesting! It's surprising that none of them show up in Mindat.

Found a rock shop in Fort Davis with a phone number. May call them this week.

Sent an e-mail to the Houston Gem and Mineral Society, along with some images. Hopefully they will respond.

Some more images:

Steve, the material you have came from a small roadcut along Texas highway 118, approximately one to two miles north of the junction with highway 166 – it was I who initiated the error of stating it was on highway 166 – sorry. I was coming up from the south on 166, but at the junction it ends and the road continues as 118, on up to downtown Kent, about 20 miles away. The land ownership is undoubtedly private on either side of the highway ROW.
The locality was found by Erich Grundel in about 2007, and subsequently visited by myself in July, 2009. Art Smith has been mentioned as the “guru” of Texas localities – I had asked him about this area, but he had been in that region only a time or two, several decades ago. His comment was “Why does anyone go to ‘West Texas’ in July ?? “. Erich revisited the area in 2010 I believe. He made a presentation about his discoveries at Rochester, and an abstract may be found here: [www.rocksandminerals.org]

The host rock is perhaps the Oligocene age (36 million years old) Sheep Pasture formation, a series of rhyolites. The matrix is hard, dense, brittle, and breaks with a sharp edge – easy to get cut. There are numerous vugs, typically thin, but up to several inches across. Some of the very fine grained red matrix also has a curious pattern of dark “spots” like a Dalmation, but I’m not sure what they represent.

The only species that I have confirmed is CRYPTOMELANE, by XRD. The material you called NONTRONITE, I have taken to be GOETHITE. Other sight-identified species are CALCITE, FLUORITE, QUARTZ, TRIDYMITE, and PYRITE, and possible BARITE. Unknowns include: black metallic hemispheres ( an Fe or Mn oxide ?); common dark brown to black, perhaps tetragonal, blocky prisms, apparently hollow pseudomorphs of ???; rare bright yellow clusters of tiny flat plates – unknown.

The material is great for micromounts – your pictures are better than any of mine.

Thanks, Tom, for your detailed response. Your description of the host rock with dark spots like a Dalmatian nails it for me. I was thinking leopards! Regarding the yellow fuzzy spheres, goethite was my first guess as stated in my original post to this thread, but after looking more closely, I saw resemblance to nontronite from Sugar Grove, WV and saponite from Horseshoe Dam near Phoenix, AZ. I could be persuaded to move back to goethite. Can I reliably ID the black and gray needles as cryptomelane? The Cliffords of Cleveland, OH contributed the material to the giveaway table at Rochester. Did they perhaps get the stuff from you or Erich?

Mindat already has a locality listed as Texas Highway 118 roadcuts, Limpia Canyon, Fort Davis ....... Should my images be posted there, or should we set up a new locality matching your description? If you send me a PM with your e-mail, I'd like to follow up with you and see if you or Erich Grundel have any more images for comparison with mine. Here's a few more:

Steve, Limpia Canyon is (mostly) northeast of Ft. Davis, on Texas route 17 - whereas route 118 goes from Kent, Texas, southeast through Ft. Davis, and on to the southeast to Alpine. I see another reference - there is a bit of the uppermost part of Limpia Canyon along route 118, just to the northwest of Ft. Davis. Maybe Norman King can give us the details of his Limpia Canyon locality. Our locality is definitely a different place.
Yes, the prolific black needles have been identified by XRD as CRYPTOMELANE. The black hollow crystal in your first of the new set of pictures is the possible pseudomorph I mentioned - hints of its being tetragonal, but then, maybe not. I do have a few of these crystals that appear to be unaltered - black, metallic, unknown.
Since the material you got in Rochester has the wrong route 166 location, I'd say it was from me, but Erich does attend the Cleveland gathering regularly, and I haven't, and I'm sure he shares egg cartons with that group. In any event lets get the locality right - it should be route 118, a mile or two north of the junction with route 166.
It should be noted that there are numerous undocumented mineral localities in this region of Texas, as Erich discussed in part in his paper at Rochester. I think Erich mentioned seven different localities in that Davis Mountains area, and there are many more. The excellent engineering of Texas highways contributes to there being numerous roadcuts, even in what most of us would consider rather featureless terrain. And in this area, if there is a roadcut, there are interesting rocks.

I added the sublocality for roadcuts in Limpia Canyon. Photo 405152 was taken 2.5-3 miles west of Fort Davis. Photo 432671 was taken in the "windy road" section farther west and somewhat north of that, in the middle of what looks on the map sort of like an "M" increasing in magnitude toward the NW. I am not 100% certain of the formation designation I made (Sleeping Lion). To someone new to the area, some of the formation descriptions sound alike. But, I hope this helps you decide how to handle this. I was collecting ROCKS, not looking for minerals, and posted the photo of sanidine-rich rhyolite. I like rock-forming minerals!

Norm King



Edited 1 time(s). Last edit at 04/27/2012 01:37AM by Norman King.

Hi, Norm!

Tom Tucker and I are working on adding his roadcut locality to Mindat. We may call it "Rtes 118/166 Roadcut(s), Jeff Davis Co., Texas" and describe it as he outlines in his posting above. We'll use his R&M reference. May I suggest that you edit your Rte 118 roadcuts locality with some of the geographic description you provide above. Maybe someone will track it down for minerals, not rocks!

Steve

Steve,

Yeah, my location information is a bit sketchy, but there was no information at all for that area at the time. I didn't have a GPS with me. In fact, I had no intention originally in doing any sight-seeing/rock collecting there or anywhere else on a hasty drive to California. I came in from Pecos on Hwy 17, and then took Hwy 118 to I-10 and Van Horn, getting in about 9:00 pm. You can see in my photos that the shadows were getting long, and I that's when I start worrying about stepping on rattlesnakes. So it was a quick and dirty tour of the area. Hope I can spend more time around there some day. The volcanic flows and associated features are marvelous.

I think I can add some detail that might help people sort out our localities. Good idea.