Black Onyx: Types, Quality, Hardness & Price Guide

Question
What are the different types of black onyx stones?
How can you find out the exact quality or the hardness?
In what different qualities are black onyx stones available and what are their price ranges?  

Answer
Have no clue...on this one.....black onyx is black onyx and to my knowledge, its not very high on the Mohs hardness scale...Onyx is very inexpensive depending on different shapes, basic shapes rectangle, round, square are abundant and easy to get.
good luck