This could be considered a Moss Agate, but the swirls of brown are so thick that there are only a few places where light shines through the slab. The brown swirls show a lot of depth. There is even a nice Drusy pocket in the corner of the slab.

It is about 7 mm thick.

Photographed wet to show details and dry to show the slab dimensions(second photo).  The dry photo is on a 10mm or 1cm to the square scale.