A lot of people believe that different crystals give off different energies, & use them for strength, healing, and other things.
Here's some examples:
Amber - protection, solar energy
Emerald - love, protects against violence
Jade - long life
Moonstone - clarity, lunar energy
Obsidian - inner strength
Tiger eye - balance
Amethyst - psychic powers, headaches
Flourite - increasing intellectual abilities
Rose Quartz - self love, beauty
I sometimes use crystals for myself & i find that they do work for me.