I have just completed a guide about fake jewellery which includes a section on the prolific amount of fake opals being sold through chinese suppliers. Much of this material appears to be a bluey sort of opalescent material that more resembles blue moonstone. It may be from a silica material that is probably man made but it is not in any way shape of form, Opal. To compare this visually I suggest that one visits one of the many reputable opal suppliers that can be found on the net by simply typing in OPALS. The instant give away is the price......real opal, from the poorer quality to the most exqisite is NEVER as cheap as being sold as the real thing through dozens of CHINESE outlets. I cannot stress this enough.
If this material was honestly produced and sold as what it is, it should still be able to command a fair price as it can be pretty......BUT ITS NOT REAL OPAL!! If you see a piece of this jewellery that you like, by all means buy it but do so knowing that it is a faked piece.
BUT I would also suggest that you tell the supplier that you doubt its authenticity and ask for a valuation certificate/proof of authenicity, to be supplied with the item. You wont get one of course but if enough people do this, the suppliers of fake jewellery may realise that we are wising up!