I guess It would depend on where they are. Where I'm at in the USA its perfectly legal to collect rocks like this, however the use of power tools such as jack hammers would be illegal unless you own a claim on the land
Diamonds. ... Diamonds are brought to the surface from the mantle in a rare type of magma called kimberlite and erupted at a rare type of volcanic vent called a diatreme or pipe. Look at the geography. You will find diamonds 💎