Probably the best rock for beginners to tumble is Agate. Here we go through steps 1-4 plus burnishing with a 3 lb rotary tumbler, with some hints and tips thrown that I have learned along the way. *** please be aware that the baking soda sometimes seems to create gas and you will have to "burp" the barrel if this happens. Otherwise, barrel can burst or leak.
Link to video where these rocks were cut/prepared from rough:
https://www.youtube.com/watch?v=V-SCHFICEPE