We recently bought this set of rocks from National Geographic in order to write this review on it, to let our customers know if it is worth buying or not. 
 
Since we already have 90% of the rocks that came in the collection, of course we will sell them on so that they are back in circulation. We like buying from National Geographic because they put funds into STEM learning and games, as well as funding wildlife initiatives in the areas they help.
 
I have personally never held a piece of this before. I had to Google whether or not obsidian can have a golden sheen to it, and it turned out it can. I don't know much about this material but it is fabullous.