I suggest you contact the GIA in London. Here is the link to their contact page: http://www.gialondon.co.uk/contact-us/
Recently, in Dubai, I heard one of the directors from GIA London speak on natural pearls. We all love natural pearls right?
Hopefully someone at the GIA can steer you in the right direction or make a good suggestion for you.
You may also try a local jewelry appraiser or try a couple of them to compare results.
First you'd want to determine if they cultured or man made. The word "Mallorqui" is very close to "Mallorca" which may indicate that they are man made Majorca pearls ....but, on the other hand, it could just be part of the name for a shop.
I hope your search for a valuation is profitable. I'm sure Yvonne would enjoy hearing about any results you find.
