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Chihuahua Trancas
  
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Kelly Jean




Joined: 14 Aug 2020
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PostPosted: Aug 18, 2020 21:00    Post subject: Chihuahua Trancas  

Hello,

I'm so happy I got these Chihuahua Trancas geodes just the other day and had a lot of fun breaking them open. In the first picture I focused on the crystal formation in the front. In the second I got the blue mineral inclusion that I am not too sure of what it is ? Calcite ?



008 - Copy.JPG
 Mineral: ?
 Locality:
Chihuahua, Mexico
 Dimensions: 4.5 cm W x 4.0 H
 Description:
 Viewed:  613 Time(s)

008 - Copy.JPG



009 - Copy.JPG
 Description:
 Viewed:  613 Time(s)

009 - Copy.JPG


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Bob Harman




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PostPosted: Aug 18, 2020 21:50    Post subject: Re: Chihuahua Trancas  

Your geode is from the Trancas Estacion locality in Chihuahua State, Mexico.

They are very interesting, often having "twisted" quartz formations so if you want more, look for previously opened examples with these quartz formations.

As to the blue area, these geodes often are a mixture of crystalline quartz and microcrystalline quartz called chalcedony. The chalcedony usually has a blue tint so that area you note is probably chalcedony.
Calcite occasionally occurs. If you are curious, put a few drops of vinegar on the area. Calcite will fizz, then quickly wash it off, but I favor that area in your geode being chalcedony.

See my examples for reference. See the bluish chalcedony area in the lower right example and look closely, in the not so good photos, to find the "twisted" quartz formations. Bob



fullsizeoutput_356c.jpeg
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 Viewed:  595 Time(s)

fullsizeoutput_356c.jpeg


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Kelly Jean




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PostPosted: Aug 18, 2020 22:36    Post subject: Re: Chihuahua Trancas  

Thanks again, Bob :)
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Peter Megaw
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PostPosted: Aug 23, 2020 14:43    Post subject: Re: Chihuahua Trancas  

The Trancas chalcedony geodes have several different styles...but almost all are spectacularly fluorescent under UV


geodes UV.jpg
 Mineral: Chalcedony
 Dimensions: drawer is 50 x 50 cm
 Description:
drawer full of Trancas geodes under SWUV
 Viewed:  369 Time(s)

geodes UV.jpg



Geode UV.jpg
 Mineral: Chalcedony
 Dimensions: 8 cm diameter
 Description:
single geode with "worms" of chalcedony protruding from the walls
 Viewed:  371 Time(s)

Geode UV.jpg



geode 1.jpg
 Mineral: Quartz and Chalcedony
 Dimensions: 6 cm
 Description:
single geode with forest of chalcedony worms, many with tiny quartz crystals on them
 Viewed:  367 Time(s)

geode 1.jpg



chih geode.jpg
 Mineral: Quartz, chalcedony and opal pseudomorphing anhydrite
 Dimensions: 12 cm diameter
 Description:
geode bristling with delicate elongate chalcedony and glassy opal after what looks like anhydrite. There are thick beds of anhydrite that the volcanics that host the geodes passed through on the way to the surface.
 Viewed:  368 Time(s)

chih geode.jpg



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