Metaphysically, Black Obsidian is known for it's protective but emotionally supportive properties. 
 
The following are the four Reiki symbols on pyramid :
Cho Ku Rei (Strength + Power)
Sei He Ki (Emotional + mental healing)
Hon Sha Ze Sho Nen (Peace + Serenity)
Dai Kyo Myo (Reiki Master Symbol)