Is the black agate or obsidian sold on Tmall true?

Not necessarily. Black agate is rare in nature and cannot be sold in batches. It is usually dyed in the market. Like the mass supply of Tmall, it is basically dyed. Obsidian is actually volcanic glass, so it is very simple to make and its composition is the same. In fact, the price gap is not big, and there is no need to distinguish between true and false.