Thank you for contacting Mearto with your appraisal inquiry.

It is a beautiful white gold necklace with opal and diamnds pendant. Such jewellery are being offered at auction on a regular basis.
The design of the pendant is very classic and thus becomes very classy and elegant. The stones are a good size with a ctw of 0,32. As you wrote the necklace is brand new I presume that it is in very good condition without signs of wear and use.
Unfortunately the price for a brand new pendant and necklace like this is much higher than the second hand sales value that the necklace and pendant represent.

I believe that this particular necklace would attract the attention of both collectors and dealers if it came up for auction.
The estimate provided is for a well-advertised specialised online jewellery auction, where I believe the Opal, diamond and white gold necklace has the best chance of realising its fullest potential. However, there is no measurement for the sentimental value you might attach to the necklace. Retail "asking prices" can be higher and vary.

Please let me know if you have any additional questions. I’m happy to help.
Thank you