gemfeller
Cave Dweller 
Member since June 2011
Posts: 4,060 
|
Post by gemfeller on Jan 2, 2023 16:14:32 GMT -5
Top slab is Sonoran Sunrise from a 2.25 lb chunk of it. You're right Bill, and in fact it came from YOU (thank you).  So am I wrong to call it Sonoran chrysocolla, meaning that Sonoran Sunrise is different ??
Patty ... realizing how little she knows about rocks more and more every day.
Sonoran Sunrise is a trade name. It differs from the scientific name. The gem trade is rife with them, especially for garnets, and it can be very confusing. I can confirm that the red portion of the slab is cuprite, the other portion bluish-green chrysocolla. I prefer the name "Chrysocolla-Cuprite" but the trade names are so well established very few would know what it referred to. Here's a link that goes into more detail:
As for telling the difference between limonite and cuprite visually I can't help you. There may be differences in spectra and through microscopic examination. Limonite is simply common rust and may have more of a brownish tint than cuprite, which is red. There are destructive lab tests but they're no help in a visual determination in a cabochon. |
|
|
|
Post by vegasjames on Jan 2, 2023 17:24:42 GMT -5
So now you have me wondering further.
Now I believe vegasjames is correct that the reddish brown of the lower slabs & my cab are limonite. When I looked up limonite the photos & descriptions of the round formations tie in perfectly.
OK, but what about the top slab- which I was told was Sonoran chrysocolla with cuprite.
How in the world can you ID the 2 different reddish brown sections ?
Cuprite vs limonite
I see what you mean James about the copper minerals and how they all get grouped together as "Chrysocolla",
but how can you tell what's what ?
Putting the slabs next to each other obviously the top one is darker - but that could mean just a better grade ?
Any tips, I'd appreciate the help.
Thank you,
Patty
The red is this stone does not look like cuprite, it looks like siderite (iron carbonate). Cuprite is generally a darker brownish red, dark red or even black. So the cuprite is likely the dark areas in the green parts of the stone.
These are examples of cuprite I collected here in Southern Nevada.
This is a siderite crystal from the same mine. Siderite is more of a light red to brick red.
The red in this stone is also siderite:
The lighter red in this stone is siderite, the darker red, almost looks purplish, areas are cuprite.
|
|
|
|
Post by vegasjames on Jan 2, 2023 17:42:15 GMT -5
You're right Bill, and in fact it came from YOU (thank you). So am I wrong to call it Sonoran chrysocolla, meaning that Sonoran Sunrise is different ??
Patty ... realizing how little she knows about rocks more and more every day.
Sonoran Sunrise is a trade name. It differs from the scientific name. The gem trade is rife with them, especially for garnets, and it can be very confusing. I can confirm that the red portion of the slab is cuprite, the other portion bluish-green chrysocolla. I prefer the name "Chrysocolla-Cuprite" but the trade names are so well established very few would know what it referred to. Here's a link that goes into more detail:
As for telling the difference between limonite and cuprite visually I can't help you. There may be differences in spectra and through microscopic examination. Limonite is simply common rust and may have more of a brownish tint than cuprite, which is red. There are destructive lab tests but they're no help in a visual determination in a cabochon. The green in Sonoran Sunrise is primarily brochantite, a copper sulfate, with very minor chrysocolla (copper silicate). Chrysocolla is very soft, and it cannot be worked easily without stabilization. The black in Sonoran Sunrise is tenorite, a copper oxide). The lighter reddish areas is supposedly chalcotrichite, an orangsh form of cuprite, but to me it does not have the orangish color of chalcotrichite and looks a lot more like siderite. |
|
|
|
Post by liveoak on Jan 3, 2023 7:48:34 GMT -5
Thank you gemfeller for explaining about "trade names", and for the article. Makes perfect sense.
Thank you vegasjames for sharing some of your expertise. I'd be lying if I said I now understood what red rock was what.
But what I did learn was that it could be numerous things.
I'd bet it's likely as 1dave was pointing out, as to the substrate ( clay, sand, or limestone) that the rock formed in.
And I probably should say, that is likely all my brain is likely to digest this morning. More Coffee first
Thank you for showing the specimens & sharing your knowledge.
Patty
|
|
