Which rock types to you split open? I am often curious to break beautiful rocks to see the inside. As an amateur I am still learning to ID rocks. What is more appreciated as a whole rock and/ or valuable?
Geodes can be broken into, although typically sawn in half.
Other specimens can be cut into slabs then lapped and polished.
The small stuff can be turned into free form cabs.
I know that sounds a little advanced but unless you can find a lapidary class/shop
your going to be limited in your quest to just field identification of your local varieties.
Depends on in what field you are. Are you looking for ore minerals? Specimens? Lapidary material?
Break open those that look interesting, that's my guide line I use. What is interesting varies a lot.