Make a platform saddle on a Paracer, place down 4 foundations near his tail, then place a cannon on it. Have the rock elemental chase you down into a stone pillar trap and shoot it's head with cannon balls until downed. Sulfur is easiest to gather and tame with, although it takes some time.
It's a bit silly that kibble tames it a lot better than rocks or sulfur because even in the dossier it says that it lives off of absorbing nearby rocks and minerals. So mabey they should make it so you have to feed them a rare mineral like obsidian what if they made it so you could tame one fast and with high effectiveness by giving one a few hundred or few thousand obsidian . or what if there kibble was made out of a combination of ores and minerals .