Each tumbled and polished gemstone is approximately 12-24 mm.   Listing is for 1 tumble.
 
Black Obsidian properties include:
Provides insight & protection from negative influences
Combats self defeating patterns
Emphasizes male qualities
Helps you integrate spirituality into everyday life
Strongly spiritually grounding
 
Chakra: Root
Zodiac: Sagittarius, Scorpio
Element: Fire
Planet: Saturn