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What is this mineral?
  
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Catahoula




Joined: 13 Mar 2019
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Location: California, USA

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PostPosted: Jul 31, 2019 14:23    Post subject: What is this mineral?  

Hello!
Several months ago I posted with what was thought to be common opal. The deeper I dig, the better the colors get. I am excavating a small pit on a lime dike in central California. These images show the mineral I am finding. Samples are 80g to well over 50lbs. They are nodules, generally football shaped and often brecciated. many are solid material similar to these images. They are located under a layer of spotch (black crumbly material). They fracture in clean lines and are similar to jasper. The pit is 50 yards uphill from a natural mineral hot spring, very low sulfur and only warm. Luster is as represented in the image. Clean shiny breaks, but the luster is lost over weeks, not years. The greens break brilliant, but fade over weeks and months to a pale color. The oranges hold luster well. There have been several samples that cut with an orange-sherbet quality of color. They do not leave a mark on paper.

This area is heavily concentrated by sphalerite (represented as small nodes covering a rock surface like chickenpox), and significant epidote (generally found as columnar in granite, often in sprays of columns).

Help me determine what this is.. Thank you!



mineral 01.jpg
 Mineral: unknown
 Description:
Southern Sierra Nevada Mountains, California
80g-50lb
 Viewed:  430 Time(s)

mineral 01.jpg


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Bob Harman




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PostPosted: Jul 31, 2019 15:11    Post subject: Re: What is this mineral?  

Based just on your photo, I think you have examples of microcrystalline quartz.....,chalcedony....probably one of the varieties of jasper. Jasper comes in a variety of colors and patterns. In your example, beside the basic color(s), there is some iron staining along the microfractures. In your examples, note the very sharp edges and area of conchoidal fracture in the upper left of the top piece. BOB
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alfredo
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PostPosted: Jul 31, 2019 16:59    Post subject: Re: What is this mineral?  

I vote for opal, based on the luster of the fracture surface, and having found stuff with very similar color and luster in Idaho that turned out to be common opal.

With the amount of it you‘re mining, you probably have enough accumulated total value already, even as cheap lapidary rock, to make an analysis worthwhile - get a definitive incontrovertible answer. I recommend x-ray by Attards Minerals in San Diego.
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Catahoula




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PostPosted: Jul 31, 2019 17:04    Post subject: Re: What is this mineral?  

Thank you Bob. Is it common for the chalcedony color to fade? Is there a way to stabilize it? I have been finding a good amount of jasper here, which is in the same family. Is the Chalcedony a marker mineral for other types of minerals? What else can I expect to find in this deposit? Having a great time exploring.
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