Hi, we like to know what beaches have pebbles, small rocks (- we already visited Pefkari, Kekes). Thank you.
Hi Daniella 
We do provide that information (and more) on Go-Thassos!
Go to https://www.go-thassos.gr/about-thassos/places and click “Beaches”
Visit any beach and scroll down to “Beach Type” (circled in red above)
https://www.go-thassos.gr/about-thassos/places/thimonia-beach
I hope this helps you with your search - please let me know, ok?