[Rockhounds] Question, Cobaltian Calcite

[Axel Emmermann]

Dave, Earl and Pete,

I almost hate myself for saying this (it's a good thing that I love myself
enough to forgive me ;-) but I actually have a specimen that comes from the
Shaba (Congo) region that is labeled as cobaltoan calcite.
It is a rather convincing purple botryoidal mass that has no collecting
value because of dents and damaged spots. I got it for free from a guy that
knows I am  into fluorescence. 
The specimen fluoresces a burnt orange under SW but much brighter under
medium wave (310 nm). That 's typical of manganoan calcite. 
Cobalt is, as far as I know, a fluorescence quencher and not an activator.
However, two thoughts cross my mind (three, actually, but one is normal for
a guy at my age and isn't about rocks):
1) Metakirchheimerite is Cobalt uranyl arsenate and contains essential
cobalt in much higher concentration than cobaltoan calcite in which the
cobalt is an accidental coloring ion. I have some Metakirchheimerite from
the type locality and it fluoresces a strong orange. We measured the
spectrum of this orange fluorescence and we found the typical tell-tale
vibrational bands of uranyl.
2) It's not because you have fleas that you cannot have lice too (an old
Flemish proverb, meaning that it is not forbidden for cobaltoan calcite to
have some manganese too besides of cobalt). My specimen fluoresces weak in
SW and on the weak side of medium strong in MW at best. Manganese is a
powerful activator if it has a good primer around and its fluorescence may
just not quite completely be quenched by the cobalt that is unmistakably
there.

So I think (not sure, just thinking) that cobaltoan calcite can indeed
fluoresce if  there's an ideal amount of manganese + primer present as
well...

Hope this helps ;-)))

Cheers
Axel


> -----Oorspronkelijk bericht-----
> Van: rockhounds-bounces at lists.drizzle.com 
> [mailto:rockhounds-bounces at lists.drizzle.com] Namens betdav97 at aol.com
> Verzonden: dinsdag 29 juli 2008 22:37
> Aan: rockhounds at lists.drizzle.com
> Onderwerp: Re: [Rockhounds] Question, Cobaltian Calcite
> 
> Hi Pete,
>    I had bought them for cobaltian calcite, but the 
> fluorescence threw me off. Is it semi-safe to assume the hot 
> pink and hot orange fluorescent ones may be mangoan, and the 
> ones that don't fluoresce, MAY really be cobaltian? They are 
> pinkish to purple in color. I'll go back and see what color 
> the ones that fluoresce are, and if the color is consistant, 
> that may narrow it down. They are from Morocco, which 
> probably may explain the mis-labeling.
> Thanks,
> Dave
> 
> 
> -----Original Message-----
> From: pmodreski at aol.com
> To: rockhounds at lists.drizzle.com
> Sent: Tue, 29 Jul 2008 4:33 pm
> Subject: Re: [Rockhounds] Question, Cobaltian Calcite
> 
> 
> 
> Hi Dave,
> 
> Let me try a first answer.
> 
> I think you have your elements mixed up a bit.? Cobaltian 
> calcite is bright vivid pink in color, but is not normally 
> fluorescent--in fact, I don't think it is ever fluorescent.? 
> It is manganoan (i.e., manganese-containing) calcite that is 
> normally fluorescent red or orange-red.? Manganoan calcite (a.k.a.
> "manganocalcite") is pale pink, but a much paler, light 
> pastel color than cobaltian calcite.
> 
> Both of these are mineralogically considered to be just 
> "calcite"; the adjectives cobaltian, manganoan just mean they 
> are varieties that contain?these metal impurities.
> 
> Sincerely, Pete
> 
> 
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