Obsidian should be cleaned after each use, just running it under cold water from your sink tap for a few moments will be enough, I find 10 seconds is enough. Dry with a soft cloth like microfiber.
Amethyst can be cleaned under cold water too, but quartz cleans other crystals so leaving them next to each other will be enough for most cases. Do not expose amethyst to sunlight, it will fade the color.
Quartzes clean themselves (except for rutilated and a few other specialty types, but pink/rose cleans itself).
If you ever want to do more cleaning, simply visualizing white-gold light or the electric blue Demonic energy scanning through it will work.
