Antiques Roadshow visited the Ulster Folk Museum near Belfast in a previously aired episode of the BBC favourite and expert John Benjamin was left very taken with an opal pendant.
John began: "Inside this very unprepossessing cardboard box is this absolutely wonderful pendant, what an opal that is, it's it's perfect.
"With opals, you often get cracks and chips and bits of wear, but I've looked at it and there's no sort of cracks and chips there at all. So let's hear a little bit more about the background please?"
The guest explained she was gifted the pendant for her 18th birthday by a family friend who had been given the item herself from her mother after she returned to Belfast from Australia.
She said "At the end of the late 1800s, early 1900s she came back to Belfast with some beautiful little opals and they were made into this jewellery. As an 18 year old you, you appreciate the beauty but it's not really your taste, but I've just kept it and I love it but I'm too afraid to wear it because it's just so beautiful."
Explaining it's provenance, the expert said: "It comes from Australia, I think South Australia. They're called black opals, although it's got this very deep, vibrant blue colour. The trick about them is to see how many different plays of rainbow colour they've got."
The owner of the piece noted the pendant had "quite a few" different splashes of colour.
"What we look for are the reds and the yellows and the tangerines those are the key colours as well as the body colour of blue and green," John remarked. "It's a very, very vibrant stone indeed.
"It's a very unusual shape. The reason I think is triangular is that I think it follows the shape of the stone in the native rock – it's got it all."
John dated the piece of jewellery around 1915 before taking it out of its box and pointing to its plain gold exterior.
"It's stamped at the back with the mark 15 for 15 carat," he continued. "Now, I'm going to say one little tiny caveat to you, with opals, sometimes rarely they put a backplate of darkening material to make them look a slightly better colour.
"I don't think you need to worry, I've looked at it very carefully with my lens and I think he's absolutely right."
The expert admitted he was "very keen" on the piece before the guest revealed she'd had it valued previously at £700 at the time she received it.
Johntold the owner the pendant was worth £4,000 leaving her gobsmacked.
"No way," she exclaimed and he added: "I think is a really, really beautiful opal and I see a lot of opals on Antiques Roadshow. Boy, this one talks to me its' a good one."
