Robin Thicke re-upped his chakra security after visiting a gem store this week ... picking up a jumbo-sized crystal used for protection.
The singer dropped by Crystalarium in West Hollywood with 4-year-old son Julian Tuesday and snagged a 2 foot high chunk of Amethyst.
Spiritual sources tell us ... Thicke spent a few thousand bucks on the stone -- which is used for purification and protection ... as well as getting in touch with the higher consciousness.
Thicke has been making a full-court press to get back with wife Paula Patton. Rock on, dude.