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Erythrite - 'Cobalt Bloom' by bmah Erythrite - 'Cobalt Bloom' by bmah
Mineral(s): Erythrite
Locality: Agoudal, Bou Azer District, Morocco

Crystals of erythrite, a cobalt arsenate mineral, varying from intensely grape-purple blades to finely acicular pinkish crystals. Specimen is from Dan & Diana Weinrich stock.

Erythrite forms a solid solution series with annabergite (i.e. structurally similar, but with a notable chemical difference). For erythrite, the defining characteristic is its cobalt content, which colors this mineral shades of purple and pink. Contrary to what you might think, cobalt in many minerals do not color them blue, but rather red to pink and purple. Erythrite is commonly referred to as the "cobalt bloom" mineral.

Photo created with a stack of 10-12 shots. Image appears still a little bit fuzzy, so I guess I should try decreasing the ISO on my camera to reduce the noise.
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Ziblink Featured By Owner Feb 26, 2015  Hobbyist Photographer
What does the solid solution with annabergite look like? I'd assume a brown or blackish color.
bmah Featured By Owner Edited Feb 26, 2015  Hobbyist Photographer
A solid solution is simply a range. I think you mean what a crystal in the middle of the range looks like?
It can be a very drab reddish brown or a very pale green.

Here's an example of a group of annabergite crystals that's probably hovering close to the 50/50 in terms of Ni and Co content:…
It's brown as you can see.

Very pale green but you can tell it's approaching a brown color too.
Ziblink Featured By Owner Feb 26, 2015  Hobbyist Photographer
I thought a solid solution was a smooth range between to or more end compositions. I know there are some minerals that will only form partial solid solutions like sodium-potassium sulfate.

An interesting little effect there, I honestly would have assumed a darker color. It's almost as if they cancelled out somehow. I've looked into iron-copper solutions and they tended to blend nicely, this is honestly curious.
bmah Featured By Owner Feb 27, 2015  Hobbyist Photographer
Well that's what I said, yes! Solid solutions are nothing but a range with an endmember on either side. What you asked was a specific color, but that varies depending on the composition. (Basically you just tripped over a bit of semantics. You're correct in your understanding.)

And I don't know if these images are entirely typical of a middle-range color. To be honest, I don't see a whole lot of semi-annabergite/erythrite.
Ziblink Featured By Owner Feb 27, 2015  Hobbyist Photographer
Which surprises me; nature's not usually one to be pure about anything. At any rate these are some top-notch specimens.
Ivan-Typhlosion Featured By Owner Feb 19, 2015
Usually when crystals form there is a physical reaction and chemical reaction. Physical for the form. And Chemical especially when color changes.
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Submitted on
February 19, 2015
Image Size
7.4 MB


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