Beware!!! there are eBay stores selling manufactured glass in the name of ancient Naga thai Relics. These are not any natural or 'cave crystals'. These are manufactured lead crystal  and they are sold as private auctions. They come in various colors from pink, red, green, black, yellow, purple etc... see picture below.

If you bid pr buy them then ask for guarantee /  certification for gemologist.
How do I know? I bought them and they definitely manufactured glass or called "lead crystal", it does not have any 'crystal' - search in wikipedia for 'lead crystal' for more information.