The short version: some stones are soft, soluble, or fade-prone. Here’s what to keep dry and what to keep out of the sun.
Keep out of water (soft or soluble): selenite and satin spar (gypsum, dissolve), malachite (releases copper, surface dulls), halite (rock salt, dissolves), and most stones softer than about Mohs 5. Hard quartz-family stones (amethyst, citrine, clear quartz, agate) tolerate a quick rinse.
Keep out of prolonged sun (fade-prone): amethyst, rose quartz, citrine, fluorite, and kunzite can lose color with long light exposure.
When in doubt: use a dry method and brief, indirect light. Browse selenite and more at a Sedona shop.