Crinoid part or pumice?

[Mahnmut]

Hello dear fellow forum members.

After a long time finally something I found myself again.

Went on a trip to some locations of my youth in the "Oberbergisches Land" region of North-rhine-westphalia.

The usual rock there is devonian Greywacke, which is much used as a very hard building material.

Crinoid stem sections of 5-10 mm diameter are abundant in spots, usually they form rust colored layers in the otherwise dark grey wacke.

Among blocks of the usual grey stuff that had at least been moved to close an old quarry I found a piece of an unusually soft, chalky yellowish stuff with a crinoid hash of very thin (about 2-3mm) segments.

It does not foam or fizz at all with acetic acid. (the dark brown spot in the pic is still wet).

The spotted clast in the middle of the closeup pic caught my eye. I wonder if it is a piece of crinoid anatomy or rather a piece of pumice.

Could this be volcanic ash containing crinoids?

Scale in cm/mm obviously.

Best regards,

J

[Mahnmut]

I loaded the pic up another time because with the scale right side up there appears to be a strong illusion, the stem sections are preserved as imprints, not in positive. The black spots are holes.

[Rockwood]

Volcanic tuff sounds right. Pumice would be long gone by now.