Years ago when the brooch was first discussed on the Royal Jewels of the World Message board some were suggesting that it contained garnets.
Unfortunately, it takes a lot of work these days to find the old threads on that board, so I cannot post a link.
One of the early photos which was posted I recollect being of where QEQM wore the brooch as a clasp to her pearls, but I don't have a photo of that.
The only photos I have are these
These are from the 1950s. I think that the other photo I was thinking of was from the 1950s also -- but of course I cannot be 100% sure.
When we first had the discussion, I looked in the newspapers and found a few references to QEQM wearing garnets shortly after she became Queen. Perhaps that is where the idea came from. Unfortunately,at the time I could not find any photos to confirm the media reports.