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[Marjolein van Braak]

These rocks were labelled Mookaite (from Kennedy Range Australia). I am not 100% sure anymore if this was the right label. Could it be?

Hardness is 6-7

[Pete Richards]

Mookaite is not an official mineral name. It is better described as the name of a rock composed mostly of silica from the skeletons of radiolaria, and is properly applied to rock from a particular locality only.

I learned this by looking it up on Mindat.org, a resource which you should add to your list as well, though its main focus is minerals and not rocks.

We too are an organization that is interested in minerals, but not particularly in rocks. If you are not clear on the difference between a mineral and a rock, please see Wikipedia.

[Amir Akhavan]

This is a either piece of agate, possibly brecciated, or it is a thin chalcedony vein or small chalcedony-lined pocked inside mookaite rock.

Agate as well as botryoidal chalcedony may look like that, because the layers sometimes weather differently and then come off in individual thin "sheets" or shards. These agates often have alternating porcellaine-like opaque and colored translucent layers. Because of chalcedony's spherulitic growth and the resulting botryoidal "habit" such agates have a very irregular and angular appearence, with sharp edges.

Alternatively, this could be chalcedony outlining some cavity in mookaite, but radiolarite and its derivatives typically are very dense, massive rocks and do not develop pockets.