Posted by Beth on October 6, 2015, 4:50 am, in reply to "The brooch"
Nellie, you have raised a fascinating question.
I had always assumed that the large central stone in the Countess' tiara was an aquamarine, but your post has made me think.
As we all know, Australia produces high quality sapphires, the colours ranging from blue to green and yellow. In Queensland yellow, green and, in particular, green-blue are common; green-blue being the characteristic shade.
Because I am familiar with the shades of green-blue found here, I can imagine that the stone in the Countess' tiara might be a sapphire.