For centuries, people of many cultures have believed in the

metaphysical properties of naturally occuring gemstones...

agate ... talisman against fear; good for dreams
amethyst ... acts as purifier, controls temperament
aquamarine… purpose and direction, meditation
carnelian ... stimulates energy
citrine ... acts as purifier, holds electricity
coral … good for averting negative intent (wear in combination with black onyx or jet for averting the "evil eye")
emerald ... amplification of understanding; balancing the aura (wear on left hand or as a pendant)
flourite ... mindfulness
garnet ... red almandine - counters melancholy; balance, peace, solitude
green grossular ... thought projection; purifier
iolite ... intuition
jade ... tranquil wisdom and peace; integrity of mind and soul (wear as protection)
labradorite ... consciousness of clear mind
lapis lazuli ... attunement to higher vibrations (wear as a pendant)
malachite ... acts as a mirror (wear when feeling happy)
moonstone ... reflection of the wearer (wear on the Full Moon) 
peridot... rejuvenation, clarity
opal ... attunement; channel for truth

ruby... mental concentration and strength (wear on left hand, but not continuously)
sapphire ... lightness and joy; best for the quiet nature
sardonyx ... good fortune
topaz ... friendship, health (helps with headaches and nightmares)
tourmaline ... compassion; maintain relationship with others
turquoise ... balance, grounding, harmony (wear on left hand or as pendant)
zircon ... independence