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Uwe Kolitsch July 04, 2019 09:07AM
Jason Utas suggested that these are tectites (indochinites).
I thought it would be pieces of the limonite-rich, water-worn gravel hosting the diamonds (note: photo wasn't made by me).

Any opinions?

Edited 1 time(s). Last edit at 07/04/2019 09:14AM by Uwe Kolitsch.
Jolyon & Katya Ralph July 04, 2019 10:06AM
Look more like tectites than limonite to me. I wonder if the title is incorrect and these are just tectites offered for sale
Keith Compton July 04, 2019 11:53AM
An article: van Leeuwan, T.M. (2014) The enigmatic Sundaland diamonds. Proceedings of Sundaland Resources 2014 MGEI Annual Convention Conference Paper, discusses the diamonds from Cempaka.

One paragraph states: "The Kalimantan diamonds are commonly found together with a mineral suite that includes corundum, diaspore, zircon, chromite/spinel, pleonaste, rutile, and rare tektite (Ubaghs, 1941)"

The Ubaghs reference is: Ubaghs, J.C.H. 1941. Diamonds in Borneo. Report held in Perpustakan Direktorat Geologi, No F 41-2 (Translated from Dutch).

So perhaps they are tektites

Uwe Kolitsch July 04, 2019 02:43PM
Thanks, Keith - very interesting.
Uwe Kolitsch July 05, 2019 07:07AM
My colleague and meteorite/tectite specialist, Ludovic Ferrière, thinks the two on the right side are tectites, but he is not sure about the piece on the left.
Jason Utas July 12, 2019 12:25AM
The specimen on the left is also a tektite. The large ~flat face with the single pit in it is an old break that exposed a bubble and has since been partly re-etched by groundwater. Faint flow-banding / schlieren are visible on the left side of the flat surface.

I looked around on Google for a similar tektite; this piece of Darwin glass is somewhat similar, although Darwin glass is generally much more vesicular than indochinites, excluding the Muong Nong layered tektites...
Uwe Kolitsch July 12, 2019 11:21AM
Ok, caption fixed.
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