FMF - Friends of Minerals Forum, discussion and message board

[Stone Mania]

It is now Pierre but I looked at it yesterday and it was fine. It doesn't say too much else other than what Pete has already said. I saw this page when I was first researching Kambaba Jasper some years ago.

PETE

Many thanks for diigging a bit deeper to see what you could find out. I know polished stones isn't a hugely popular topic here.

Regards,

Laurence

[James Catmur]

Pierre

The link, which works for me, is

https://www.madagascarminerals.com/pd-crocodile-jasper-rough-100-lb-lot1.cfm

I removed the extra ',' and corrected Pete's version (and yours)!

James

[Pierre Joubert]

[James Catmur]

Pierre

Just in case you had not seen them - this is Cotham Marble, which is stromatolitic

https://www.bristol.ac.uk/centenary/look/cabinet/cotham-marble.html

James

[marco campos-venuti]

Nice thread. But we have to talk with pictures, because most of us are Mineralogists and are no familiar with slab material.

Some clarifications:
1-Stromatolite is a generic name for rock build up by bacteria as coral is for Anthozoa. Many different structures are presents.
2-Stromatolite doesn't means Precambrian, there are many living examples as there are many Neogenic fossils.
3-Kabamby is the name for a variety of Ocean Jasper found in northwestern Madagascar, in the Analalava district of the Sofia region in the former province of Mahajanga. Ocean Jasper has been mined in two location: Marovato and Kabamby, 10
miles distant one from the other. Kabamby gives material more opaque and green in color, while Marovato is characterized by more Chalcedony rich, translucent material full of colors.
4-Kabamby Ocean Jasper is often confused with Kabamba Jasper, a green and black stone with eye shaped patterning from the area of Kabamba in the west central Bongolava region, in central Madagascar west of Antananarivo. The place is also commonly spelled as Kambaba. It is also sold under the trade name Crocodile Jasper.

Despite orbicular Kambaby Jasper and the Kambaba eyed Jasper are similar they have two different origin.
Kambaby Jasper is an orbicular jasper formed by alteration of a former obsidian
lava flow. orbicular structures are devitrification pattern as in Snowflake Obsidian. Kambaba Jasper is a oncolite stromatolite build up by bacteria and replaced by silica.
The difference are that orbicular spherulites of Rhyolitic Jaspers, as Ocean Jasper, are strictly spherical and in Oncolitic Jasper have a more "biological" potato shape. Also the organization of spherulites in Rhyolitic Jaspers follow alignments of the original lava flow, while in Oncolitic Jasper they are more randomly distributed.
A material similar to Kambaba Jasper is the Chambless Limestone, found in
California in the Marble Mountains, Mojave Desert. It is a green rock constituted by oncolites of the genus Girvanella and is dated at Lower Cambrian.

[Stone Mania]

Hey Marco,

Thanks for your detailed reply regarding Kambaba/Kabamba Jasper, it's so much more than I expected and it seems to offer a logical explanation as to why there's so much confusion about it.

One think I'm curious about is you say Kabamby Ocean Jasper is often confused with Kabamba Jasper which is from the area of Kabamba in the west central Bongolava region of central Madagascar and it's also commonly spelt as Kambaba but having looked at several maps of Madagascar and having also searched online, I can find no mention at all of any place by the name of Kabamba or Kambaba anywhere in Madagascar.

Before I publish anything I want to make sure I've got the facts straight so I'm hoping you can offer some further clarification on this.

Many thanks for your time and expert knowledge.

Regards,

Laurence

[marco campos-venuti]

Hi, I worked for more than ten years in Madagascar and I understood that it is in Africa and it is an Island, two factors making it quite different. In Mada there is one city, Taná, the capital and 4 roads. One goes North, one South, West and East. It so simple.
All rough materials go towards the capital at the center of the 4 roads where people know very little about the bush. When a deposit is worked by farmers in the middle of nothing, they bring their findings at the nearest weekly market that is on one of the four roads. All material found in an area results as to have been found in a location corresponding to the name of this market.
Mount Ibity and Betafo are two location famous for tourmalines, but they are just names of market villages. They collect minerals coming from hundreds of different pegmatites and different claims.
The Kabamba Jasper comes from Tsiroanomandidy in the region called Bongolava. I never was there, but I know it is quite a small region that you can use as a location. It is more or less the size of Paris Metropolitan Area. It is better than to say that a tourmaline comes from Minas Gerais which is larger than the whole of France!

[Stone Mania]

Many thanks once again for your help. It's greatly appreciated.