The aquamarines worn most often by the Queen have become quite well known - the Aquamarine Clip Brooches, and the pieces of the Brazilian Aquamarine Parure - but they aren't the only aqua jewels in the collection. This aquamarine brooch contains a rectangular aquamarine stone surrounded by a delicate diamond laurel wreath, described in Leslie Field's The Queen's Jewels as "two curved diamond branches".
Unfortunately, that diamond detail disappears when worn on a patterned fabric as the Queen has done. The brooch also looks much larger when seen from the side or on video, when its depth is revealed. But when worn on a patterned fabric, as The Queen has done in some of the recent outings of this brooch (and there are not many, as this is a rare one), it can appear small.