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What are your favorite finds from the 2010 Tucson Show?
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Pete Modreski
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PostPosted: Mar 02, 2010 20:18    Post subject: Re: What are your favorite finds from the 2010 Tucson Show?  

A few slightly "offbeat" things in exhibits that I enjoyed seeing at the Show...


PICT0181 NM feldspars.jpg
 Description:
gem feldspars from New Mexico, sanidine (moonstone) and plagioclase (gem labradorite), from Virgil Lueth's case from the N.M. Tech Geology Museum
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PICT0181 NM feldspars.jpg



PICT0176.JPG
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Barb Dutrow (LSU) created a display of mineral assemblages in metamorphic rocks, each with its calculated temperature, pressure, and depth of formation!
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PICT0174.JPG
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is this perhaps the first time a phase diagram has been posted on the Fabre Minerals Forum?
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"Natural, Single-Mineral Sands"
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vic rzonca




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PostPosted: Mar 07, 2010 21:51    Post subject: Re: What are your favorite finds from the 2010 Tucson Show?  

Got this from Great Wall Minerals, I found the contrasts stunning.


IMG_3372-1.jpg
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Smokey quartz with microcline 7x15cm.
China
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IMG_3372-1.jpg


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PostPosted: Mar 08, 2010 00:38    Post subject: Re: What are your favorite finds from the 2010 Tucson Show?  

That is interesting looking vic.
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PostPosted: Mar 08, 2010 05:08    Post subject: Re: What are your favorite finds from the 2010 Tucson Show?  

Very nice Vic. For some reason feldspar seem to be underappreciated, except for amazonite.
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PostPosted: Mar 08, 2010 06:37    Post subject: Re: What are your favorite finds from the 2010 Tucson Show?  

Very nice combination and typical for many miarolitic cavities in granites where the quartz crystals are smoky beacause of the backgorund radiation in the granite.
John, also white feldspar crystals may command high prices. A white microcline from Brazil was posted on the irocks website yesterday and sold at once for USD 6.500.
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PostPosted: Mar 08, 2010 08:32    Post subject: Re: What are your favorite finds from the 2010 Tucson Show?  

That may be a rare exception because in my experience at shows feldspars, very nice ones in fact, tend to me modestly priced and hard to sell.
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vic rzonca




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PostPosted: Mar 08, 2010 08:34    Post subject: Re: What are your favorite finds from the 2010 Tucson Show?  

Could one of you give me a simple explanation of miarolitic?
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PostPosted: Mar 08, 2010 09:20    Post subject: Re: What are your favorite finds from the 2010 Tucson Show?  

You can find the following definition in Wikipedia:

"Miarolitic cavities (or miarolitic texture) are typically crystal lined irregular cavities or vugs most commonly found in granitic pegmatites, but also found in a variety of igneous rocks. The central portions of pegmatites are often miarolitic as the pegmatite dike crystallizes from the outside walls toward the center. The volatile portion of the magma is gradually excluded from the forming crystal phases until it becomes trapped within the body and forms the cavities which often contain minerals of elements incompatible with the typical silicate granitic mineralogy."

In plain language this means that miarolitic cavities are formed by residual vapor/gas in magmas that may contain a diversity of mineral forming elements. Feldspar has a much higher melting point (ceramics compared to glass) -- and will crystallize first, followed by quartz in the most simple mineral assemblages of such miarolitic cavities in granites.

They are of great interest to mineral collectors not only because well formed and large crystals can form in such cavities, but also because they may host a number of gem minerals and rare minerals in exceptional crystals.

Knut
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PostPosted: Mar 08, 2010 09:21    Post subject: Re: What are your favorite finds from the 2010 Tucson Show?  

Keldjarn -- Don't believe the prices on that site when a piece sells. And don't believe they all sold immediately either. That was the "list" price, but not necessarily the selling price. And we have seen some pieces go up on that site in a new listing that we knew were sold long before they were posted. Its all marketing.

John is right that most feldspars are relatively modestly priced unless they are blue or have another mineral in association that drives up the price.
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PostPosted: Mar 08, 2010 09:33    Post subject: Re: What are your favorite finds from the 2010 Tucson Show?  

Joan, of course you and John are right that except for amazonites, yellow gemmy orthoclase from Madagascar and crystallized Mexican moonstone, feldspars are usually cheap - even in good crystals. I only wanted to show that these days when even groups of pyrite crystals are known to have been sold (at auctions) for more than 50.000 USD, it is sometimes surprising what some specimens are sold for. I know also there is a lot fo marketing tricks on the web, but even if this specimen was sold for 20 % of the price mentioned, it would have been a very expensive white microcline !
Knut
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PostPosted: Mar 08, 2010 12:48    Post subject: Re: What are your favorite finds from the 2010 Tucson Show?  

Vic, do you have a specific locality for the Chinese smoky quartz-feldspar combination? I'm just curious whether it came from the miarolitic granite cavities at the Tongbei (Fujian Province) spessartine mine? Some of the specimens from there do not have the spessartine xls, while others have a variety of other interesting minerals with the quartz and feldspar.
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PostPosted: Mar 08, 2010 15:18    Post subject: Re: What are your favorite finds from the 2010 Tucson Show?  

Woody, Namping of Great Wall said it was from either Tongbei or Yunling, I've misplaced the label, I may have to wait till Denver for the exact location info. Thanks for the miarolitc cavity expanation Knut, I've collected in them for years so it's good to know what the beta is on them.
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