Oolitic Chert

Aha! This is the sample Hazel found on the Aliakmon,
and it's a beauty!

The matrix is Fe-rich silica, now chert.

Each of the roundish ooliths are about 0.5 cm, and
their centers consist of nuclei of various sorts.
Some are greenish and look like rock fragments, others
whitish and perhaps shells. Or even shark teeth fragments?This one needs a good
microscopic examination.

Ooliths are merely little mudballs rolled around by low,
steady waves. Most form in carbonate (coral) sands in shallow waters and then become oolitic limestone.,
But these are indeed siliceous, causing a great deal of sparking when being sliced with the rock saw. This implies a much
greater depth. I'll read up on these and get back
to you.

The width of the sample shown is about 2 cm.