FMF - Friends of Minerals Forum, discussion and message board

[Stone Mania]

So I've come to my favourite minerals forum once again to pick the brains of the expert members who usually manage to answer my questions!

I've been writing another article for the "Minerals" section of my website this time on Kambaba Jasper and am hoping to get a few opinions about what kind of rock this actually is. I have always been led to believe it's a stromatolite which features black orbs of fossilized algae and that it's sedimentary but when I recently started looking to see if I could add anything new about it to my page, I stumbled across a comment on another forum which totally disputed this.

Whilst I've included the comment in the article on my website, I don't want to post a link to it here but in a nutshell, the author said Kambaba Jasper is volcanic so it's not a jasper at all, it's an igneous rock and the green colouration is caused by quartz, the black orbs are feldspar and in mineral composition it's similar to Eldarite. Eldarite when polished is apparently known as Nebula Stone and the two have a very similar appearance with the only real difference being the colours are the opposite way around.

So I'm interested to hear others' opinions about what Kambaba Jasper actually is.

Any help as always would be greatly appreciated.

Thanks,

Laurence

[lluis]

Hi, Laurence

Well, think link to Mindat would say far more that I could say.
First time I have heard about Kambaba Jasper.....

https://www.mindat.org/mesg-55-85320.html

Besides, Kambaba jasper is sedimentary (fossilized dumps of algae...), so *no* volcanic

With best wishes

Lluís

P.D.: trouble in creating and using names that are not approved by IMA is that it creates a big mess. And I am not certainly a fan of IMA, but better a bad IMA that to no have IMA at all...

[Stone Mania]

Hi Lluís,

Thanks for your reply, I was actually just reading that thread and commented on the very bottom of it some time ago and those "in the know" do seem to completely disregard any association at all between Nebula Stone and Kambaba Jasper and they seem to know what they're talking about.

I'd completely forgotten that I'd posted that comment and was just coming back to edit my comment here and to say I think I've found the answer I was looking for but because you commented, I was unable to edit it!

Thanks anyway.

Warm regards,

Laurence

[Vinoterapia]

As per the comments in the Mindat thread is apparent the the so-called Kambaba jasper is actually a rhyolite and not a stromatolite.

[lluis]

Hi, Vinoterapia

Maybe I loss anything

But if you read
"KAMBABA JASPER is a sedimentary stone that is FOSSILIZED BLUE GREEN ALGAE (prokaryotic bacteria)."
And a Rhyolite is a volcanic rock.

Well, what is it?
If sedimentary not volcanic.
And that returns to the question of Laurence: volcanic or sedimentary? (to my eyes, looks not as a rhyolite, at least the ones I have seen from Utah with red beryl and topaz and bixbyite....)

Uhhhhhhh??????

With best wishes (troubles of placing names that are not IMA approved.... :-( )

With best wishes

Lluís

[Stone Mania]

I thought I'd found the answer that I was looking for but there's so much information on the Mindat thread that it's difficult to work out what stuff is being ridiculed and what's genuine and the most relevant section is in German so I can't understand that at all!

And it seems Lluis is also slightly confused about this stone now as well!

I do have a detailed description on the page on my website from another forum but I don't want to post any links here but feel free to take a look if you're interested. It's on the Kambaba Jasper page of my Minerals Section.

It just goes to show how much incorrect information about minerals is posted online. Very happy that I can usually get to the bottom of things when I come here though :-)

Thanks,

Laurence

[James Catmur]

Laurence

Any similarities to Cotham Landscape Marble?

James

[Vinoterapia]

Hi Lluis.

Among several comments that suggest that the Kambaba rock is not a stromatolite, there is a post in German that is translated into English as follows (using Google translate):

"For some years, two rocks have been offered in Germany under the name Eldarit, which differ visually clearly. The first variant comes from Mexico and consists of a (almost) black rock with green dots and circles (A). As some of the people at the sight of this rock felt like galaxies or star nebulae in the universe, it grows in the USA the trade name "Nebula-Stone".

Thin-section and micro-probe analyzes showed that the rock consists of a dark matrix of quartz and alkali feldspar (anorthoclas). Embedded in it are light-green amphibole aggregates (Riebeckite to Arfvedsonit), which are surrounded by fine-grained pyroxenes (Aegirin). The development has not yet been fully clarified, but it is probably a volcanic rock that has been overwhelmed by a weak metamorphosis. Eldarit in the described training is often the United States, in Germany very rarely traded.


In Germany you almost always get a rock under this name, the color distribution of which is just the opposite of the Mexican Eldarit. This rock comes from Madagascar and is also referred to as Kabamba- (synonyms: Kambamb-a or Cambaba) - "jasper" (B). The opinion expressed by various companies in Madagascar and the USA that it consists of fossil stromatolite algae is definitely wrong.

Thin-film and X-ray diffraction analyzes by the EPI Institute have shown that it is by no means a kind of jasper but a volcanic rock. In the green ground mass of quartz, pyroxene (Aegirine), as well as soda and potash spats, circular aggregates are arranged from very small amphibole needles (Riebeckite to Pargasit).

In the mineral stock, the two rocks are very similar. They differ primarily in the quantity of the individual minerals, their distribution and possibly also the type of the starting rock. From a mineralogical point of view, however, both rocks are so similar that the trade names Eldarit and Kabamba can be accepted as equivalent synonyms. Since no jasper could be detected in any of the examined samples, the term "Kabamba jasper" should be avoided and replaced by the term "Kabamba stone".

You will find detailed information about this important rock in our newsletter archive. "



Regards.

José Luis.

[Stone Mania]

Hey James,

No it's nothing like that at all, it's almost always the same as in the image I posted, colour and markings vary minimally.

Regards,

Laurence

[Stone Mania]

So that German article is what the guy in the other forum that I visited posted.. Here's his translation:

The EPI (Institut für Edelstein Prufüng) or Institute for Gemstone Testing in Germany published a detailed report in one of its bulletins. Unfortunately the bulletins are only available to members (and only published in German). Nevertheless, paraphrasing a bit from their findings, thin-section and X-Ray diffraction analyses have shown that the kambaba material it is not a type of jasper at all, it’s volcanic. The green groundmass is composed mainly of quartz, pyroxene (aegirine) with orbicles of alkali feldspar embedded with streaky aggregates comprising tiny needles of amphibole (riebeckite to pargasite). The formation is not fully understood but it’s most likely a volcanic rock that has been “overprinted” by a weak metamorphism. In mineral composition it’s very similar to a rock originating in Mexico that’s generally referred to in the lapidary world as “Eldarite”, although the colouration is the reverse of the Madagascan material in that Eldarite has a dark groundmass and pale orbical patterns (whereas Kambaba Jasper has a pale groundmass and dark orbicles). Eldarite is also known in America as “Nebula Stone” since, when polished, the patterns resemble nebulae in outer space. The two rocks are nevertheless sufficiently similar from a mineralogical point of view that the EPI recommends the names “Eldarite” and “Kambaba” should be regarded as synonyms. They also advise that the term “Kambaba Jasper” should be replaced by the term “Kambaba Stone”.


The reason I had doubts about this text was because in the mindat forum (which is not the same forum where this article was posted), the people who seem to really know what they're talking about say that Kambaba Jasper and Nebula Stone are two COMPLETELY different rocks which share nothing in common at all and this article says from a mineralogical point of view, they're very similar.

[Pete Modreski]

I'd like to add my "two cents" about this discussion. There are many points of possible confusion about the rocks being discussed here! It does seem quite clear that the two kinds of green rock studied in the German paper, definitely are volcanic, not stromatolites or any other sedimentary rock. However, I think it is less clear, whether the rock commonly being sold as "Kambaba Jasper" is necessarily the same material as what they studied.

Much of the problem exists whenever one is trying to discuss or describe stone material, without seeing the actual geologic locality from which it is produced. In fact, I see that the Kambaba [jasper] isi sometimes described as being from Madagascar, sometimes from South Africa. Geologists all know--that there is no substitute for seeing a rock in large quantities and in its actual geologic location and context, to be sure one is making the correct interpretation about what it is and how it formed.

In fact, the term "jasper" itself is used and interpreted in different ways, even in the formal geological literature. The AGI Glossary of Geology originally defined it as "A variety of chert associated with iron ores and containing iron-oxide impurities that give it various colors", but then goes on to define "jasperization" as "The conversion or alteration of igneous or sedimentary rocks into banded rocks like jaspilite by metasomatic introduction of iron oxides and cryptocrystalline silica".

The bottom line is, I think most geologists and mineralogist would define "jasper" as any igneous or sedimentary rock that has been thoroughly silicified by replacement with cryptocrystalline silica, with inclusions of iron oxide coloring material (of any color).

That being said, it "appears" that the Kambaba "Jasper" is indeed a type of jasper, originally a volcanic rock, and that it only resembles the pattern seen in stromatolites. But one probably has to be cautious, because all of the material being called by that name, may not necessarily have originated in the same place. We are dealing with stones being marketed by different sellers in different ways, and "who knows" what variety of material might be included in this!

I could probably try to add more, but I think I'll leave my comments at this.

Good wishes to all,
Pete

[lluis]

Truly agreed with Peter!

With best wishes

Lluís

[Stone Mania]

Thanks Pete, I tend to agree with what you've said as well. To be honest, we've been buying minerals in South Africa for some years and I've never found any Kambaba Jasper that comes from there, it all comes over from Madagascar.

Regards,

Laurence

[Pete Modreski]

I did a little more (successful) browsing about "kambaba" and I did find this and thought I'd share it, about its source. This is from Norcross, a company that mines and sells a great deal of rock/gem material from Madagascar.

It comes from their "Crocodile Jasper" mine, but their pictures of the material clearly show that it is the same as what's commonly marketed as Kambaba Jasper. (I see that the rough material looks much lighter in color than after it's been polished.) Their website, at https://www.madagascarminerals.com/pd-crocodile-jasper-rough-100-lb-lot1.cfm says,

"Crocodile Jasper(TM) Rough from the Norcross-Madagascar (NMG) Crocodile Jasper mine. Others have referred to this stone as Kambamba Jasper, named after the river locality beside the quarry."

This is as much as I've been able to find explicitly online about where the material comes from--and it took a good bit of searching, even within the Norcross website, to find this description.

P.S., I realize that we don't usually spend this much space writing about "polished stones" here on the Friends of Minerals Forum, but, well, the topic just seemed interesting, and it does appear to be an interesting rock type, geologically speaking.

[Pierre Joubert]