Since i can't link other links.
supposedly it is illegal to harvest seriyu stone directly from japan since year 2008. other rocks may be or may look like seriyu stone that is why i posted that it may be ryuoh stone.
If you google about seriyu stone you will find a bunch of forums suggesting the same idea.
I am no expert... i am just offering my +1.
I would hate to see another member to purchase something that possibly be mis-labeled and mis-represented.