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Peter Megaw
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Joined: 13 Jan 2007
Posts: 963
Location: Tucson, Arizona
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Posted: Aug 20, 2013 13:39 Post subject: Re: Endomorph or Pseudomorph? |
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Just got some new polished Crazy Lace slabs that show the differential/asymmetrical infilling patterns across the line representing the original calcite crystal.
Nice examples of the phenomenon...
Thanks to Jeff Galinger (Rock of Ages, Bailey Colorado) for the slabs and polishing
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Crazy lace agate...chalcedony ps calcite Sierra Santa Lucia, Chihuahua, Mexico 12 x 4 cm Slabs clearly showing asymmetrical/differential "open-space" (or perhaps gel filing) on opposite sides of the original calcite crsytals |
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Crazy lace agate...chalcedony ps calcite Sierra Santa Lucia, Chihuahua, Mexico 9 x 6 cm really strong asymmetry in this pair. |
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marco campos-venuti
Joined: 09 Apr 2014
Posts: 207
Location: Sevilla
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Posted: Jul 22, 2014 12:46 Post subject: Re: Endomorph or Pseudomorph? |
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I would add some theory about the genesis of Lace Agates as the Crazy Lace is.
Lace Agates:
-are vein agates formed in open systems
-show alternating banded chalcedony and others minerals such as quartz, calcite, aragonite or Baryte
-are often associated with ore deposits
Lace Agates are formed by two different mineralizing fluids, a concentrated one and a diluted one:
1-During the dry season, highly saline waters coming from a possible salt lake are responsible for the alkaline and colloidal solution that form the bands of chalcedony.
2-During the rainy season, a diluted solution, possibly heated by a hydrothermal system, often associated with a volcanic caldera, is responsible for the crystallization of quartz or other low temperature minerals.
There is more information in my book: Genesis and Classification of Agates and Jaspers: a New Theory by Marco Campos-Venuti:
https://www.agatesandjaspers.com/
(link normalized by FMF)
I don't know the geology of the Crazy Lace deposit, but I suspect there is a hydrothermal system associated with the ore deposit and it is highly possible it's related to a buried caldera system. On the other hand, a close salt lake is quite common in the Chihuahua Desert, nowadays or in the past.
So there is an alternation of silica waters that form banded agate and diluted waters that crystallize calcite or quartz. The more common in the Lace Agates is quartz alternated with chalcedony. When the colloidal solution comes again, the calcite is out of its stability field and is altered.
There are 2 or 3 phases of calcite in the Crazy Lace deposit and 4 or more of quartz.
Here some more picture of Crazy Lace, a really wonderful material for specimens, not only for cabochons.
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Crazy Lace Agate Chihuahua, Mexico 10 cm |
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Crazy Lace Agate Chihuahua, Mexico 25 cm |
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Crazy Lace Agate Chihuahua, Mexico 15 cm |
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Crazy Lace Agate Chihuahua, Mexico 30 cm |
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Crazy Lace Agate Chihuahua, Mexico 9 cm |
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Crazy Lace Agate Chihuahua, Mexico 35 cm |
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marco campos-venuti
Joined: 09 Apr 2014
Posts: 207
Location: Sevilla
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Posted: Jul 22, 2014 13:21 Post subject: Re: Endomorph or Pseudomorph? |
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Another Crazy Lace with possibly Aragonite in the place of Calcite.
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Crazy Lace Agate Chihuahua, Mexico 9 cm |
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Dale Hallmark
Joined: 16 Jun 2014
Posts: 189
Location: Texas Panhandle
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Posted: Jul 22, 2014 13:22 Post subject: Re: Endomorph or Pseudomorph? |
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Thanks for posting these. Very nice material! I was never much of a fan of polished slabs but you have changed my opinion :-) I will have to shop around and educate myself.
Dale
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Peter Megaw
Site Admin
Joined: 13 Jan 2007
Posts: 963
Location: Tucson, Arizona
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Posted: Jul 22, 2014 14:05 Post subject: Re: Endomorph or Pseudomorph? |
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Dale...I felt much the same way when all I saw of this stuff was cabochons. Slabs, and working in the neighborhood, definitely changed my mind. There are a few dealers out there who specialize in agate slabs...for those of us old enough to remember browsing LP racks in the record store, the skills for flipping through slabs are the same!
Marco...there is no question about the link to the nearby hydrothermal ore deposit...some of the crazy lace pieces contain galena and others tetrahedrite (and weep copper oxides). Many contain specularite and nearly all have Baryte, which is a common gangue mineral in the nearby sulfide mineralization.
Geologically the "Laguna Lace" agates are infillings of collapsed paleo caves developed along a thrust fault. The caves were repeatedly filled with scalenhedral calcite and bladed Baryte (contemporaneous?) that was in turn repeatedly brecciated, both before and during deposition of various forms of silica. The attractive lace agates are only one manifestation of jasperoid alteration in the district. Virtually every major fault is marked with jasperoid, in some cases with Baryte with sporadic tetrahedrite. There ae places closer to the mineralization where multi-stage silica introduction ranges from cryptocrystalline chalcedony to coarse crystalline quartz (xtals to 5 cm).
There is good reason to believe that the agatized thrust fault is directly connected to the plumbing of the nearby ore deposit, which in turn can be traced from massive replacement sulfides to intrusive related skarn over at least 5 km laterally and 1 km vertically. The skarns and replacement sulfides show multiple stages of mineralization and brecciation that may correspond to the stages seen in the agates. Comparison with other CRD-skarn systems indicates there are fundamental pulses and stages of intrusive emplacement that drive the whole thing. Overall, the geology indicates the agates are indeed a peripheral alteration style to the integrated magmato-hydrothermal mineralization system. It is quite likely that the collapse breccias that host the agate are the products of episodic hydrothermal "karsting"
There are volcanic rocks (welded ash-flow tuffs and rhyolite flow domes) in the area (5 km away) but no recognizable caldera nearby. There are at least 2 mapped calderas 20-30 km to the south. Although there is an evaporate-rich dry lake 30 km to the north (Laguna Guzman, source of large sand gypsum groups), it is a relatively modern feature compared to the probable 30+ Ma ore deposit. We have seen no sign of evaporate rich layers in the alluvium...and we have LOTS of holes through it.
However, evaporates definitely exist down-section beneath the host limestones and are known to be extensive in the Chihuahua Trough (Basin) to the east. Sulfur isotope work indicates a significant basin brine component in the ore fluids and we have hypothesized that the big deposits are big because of a hybridization between magmatic and basin brine (MVT-like). This story was published in SEG Special Publication #4 in 1996.
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Crazy Lace Agate Sierra Santa Lucia, San Buenaventura, Chihuahua, Mexico 6 x 16 cm Slab of crazy lace showing prominent Baryte-rich fragment within multi-stage agate fillings |
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Crazy lace agate pits, all developed along a thrust fault |
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crazy lace agate cementing paleokarst breccia |
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Dale Hallmark
Joined: 16 Jun 2014
Posts: 189
Location: Texas Panhandle
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Posted: Jul 22, 2014 14:14 Post subject: Re: Endomorph or Pseudomorph? |
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I remember flipping through LP's. I also remember working a deal with the Jukebox dealer for all his 45's as he replaced them. Wish I still had them.
Dale
Peter Megaw wrote: | Dale......for those of us old enough to remember browsing LP racks in the record store, the skills for flipping through slabs are the same!
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Peter Megaw
Site Admin
Joined: 13 Jan 2007
Posts: 963
Location: Tucson, Arizona
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Posted: Jul 22, 2014 14:21 Post subject: Re: Endomorph or Pseudomorph? |
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I'm still a vinyl junkie...the squirrel gene manifests itself in many ways!
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marco campos-venuti
Joined: 09 Apr 2014
Posts: 207
Location: Sevilla
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Posted: Jul 22, 2014 17:48 Post subject: Re: Endomorph or Pseudomorph? |
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Peter you are a crack!! I never found so much information about Crazy Lace in years of investigation, thank you very much.
I just want to add a picture of a specimen of a quite recent material called Sangria Jasper, that is found together with the Crazy Lace. It is a nice brecciated jasper mixed with banded agate. A real multiphase multisilica multibed event.
Dale, I was a purist of minerals and crystals some 15 years ago, when I met a guy in Quartzsite called Pat McMahan (or the sagenite man).
He has a page where he shows his passion for sagenite, plume, moss and other kind of agates with inclusions.
https://www.agateswithinclusions.com/
(Link normalized by FMF)
At that moment I realized that polishing an agate does not change it, but allows one to look inside the stone. This is the topic of collecting: look inside stones. Now I mix together crystals and polished slabs in my collection, and I guarantee you that if you start to buy some agates, you will find colors, oddities and a lot of mineralogy.
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Sangria Jasper Chihuahua, Mexico 35 cm |
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20954 Time(s) |
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Dale Hallmark
Joined: 16 Jun 2014
Posts: 189
Location: Texas Panhandle
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Posted: Jul 22, 2014 18:40 Post subject: Re: Endomorph or Pseudomorph? |
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Another very nice example.
I'm not really a purist in that I restrict myself to classic minerals and crystals. I like rocks too and actually have very few mineral samples with obvious crystal faces. What I have had a preference for are rock and mineral samples that are totally natural and haven't been altered by man in any way. Not cut or polished.
Although I have no rule that I haven't broken :-) I have recently been looking at some banded minerals like Rhodochrosite. The specimens I like so far have been out of my league financially and not as intricate or dramatic as these lace agates.
Fun to look at and dream :-) !
Dale
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Peter Megaw
Site Admin
Joined: 13 Jan 2007
Posts: 963
Location: Tucson, Arizona
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Posted: Jul 22, 2014 19:30 Post subject: Re: Endomorph or Pseudomorph? |
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The agate slices are a LOT cheaper than good rhodo slices
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