rich Wrote:
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>"opal-A or something like that"
>-- I'll come back to the asbestos. I again thank
>you for continuing this dialog.

>Barsoum had proposed diatamaceos earth (a common
>additive in cement) as an ingredient. A common
>impurity in diatamaceous earth is opal-a.

It occurs in limestones too... as lepispheres, etc. I think the diatomaceous earth with its opal-A etc. is support to get dissolved to form primary silica cement, Which the silica in the Lauer sample is not.... Why is it forming lepispheres and other chert-like structures in isolated interstitial locations within the porous limestone and not as a primary cement? The primary cement in the Lauer sample, as indicated from Harrell and Penrod (1993) petrographic analysis, is calcite spar and microspar.

>What
>are your thoughts on this ingredient?

There is also a lot of opal-CT in the Lauer sample too... thus the XRD results and presumably from Barsoum et. al. (2006) Table III with its presumably lower Mg values. This also in consistent with a natural limestone... as we see from Jana's presented analysis.

Archae Solenhofen (solenhofen@hotmail.com)