Although not strictly classed as a crystal, Obsidian is a very useful stone to have in your collection.
Often called “the Truth Stone”
Zodiac sign: Capricorn, Sagittarius, Scorpio
Solar System: Pluto, Saturn
Goddess: the Morrigan, Pele
Issues/Intentions: Acceptance (especially of that which is hard to accept), aggression, balance, clarity, distressing times, fear, grounding, manifestation, moving on, negativity, protection, release of emotional ties, release of “hidden” issues, spiritual development, transformation, worrisome times.