Black obsidian has been used for centries for many things. Because of the shine, it was used as a mirror before mirrors were created! It is made of lava rock that didn't have time to cool to glass! Because it is created from the depths of the earth, it is associated with the root chakra. It is also said to be a great protector and cleanser of the aura. I personally recommend keeping a piece of black obsidian near your front door or where you often sit with visitors to talk. It keeps the negative energy down and cleanses everyone near it! It is associated with Saturn, Scorpio, and Sagitarrius. 
Tower A measures at 3.75 inches tall
Tower B measures at 4.5 inches tall
Tower C measures at 4 inches tall