I have ancient rings with semi presious stones and I would like to sell them or donate them for tax purposes How do I determine their crrent value when I offer them to housing works?

This isn't really a question about the Housing Works Thrift Shop, but you should probably search on eBay to see what similar rings are going for. Otherwise, you could hit up a pawn shop and hear what they have to say.

Take them to someone who appraises jewelry

If they are antique, take them to an appraiser and have them valued formally. They will be able to generate the correct paperwork for you to submit to the IRS and to the charity.