This a Large Vintage 8 Carat Gold & Massive Specimen Opal Pendant/Brooch, I would think from the 1960’s/70’s.
It features a huge natural opal from the Lightning Ridge mines of Australia. The opal is domed, 25mm by 19mm and of approx. 28 carats. The opal has a grey background colour with the lower portion flashing mainly green, with a red and yellow band separating it from a plain grey upper portion. This type of opal is often referred to as a “picture opal” as it is reminiscent of something or other, which in this case, looks to me like a “sunset over water”.
The piece can be worn as a pendant or brooch and is stamped “333”, which is a German standard for solid 8 carat gold. It is 30mm by 24mm overall, with the hinged suspension loop a further 10mm high.
It is in excellent overall condition, with no damage/repair or obvious signs of wear.
A beautiful and unusual large piece, for those who like something different and exclusive in their jewellery.