Use small natural stone archways to trap it, there are a few on Scorched Earth map, as the natural stone blocks the rocks it throws and won't take dmg and prevents it from making other types of attacks. Now you have a nice and still Elemental to shoot at in safety. Pillars work well but it can change aggro and you'll have to readjust your aim.
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 .