I have read there are 27 tourmalines in St Edward's Crown, the one used to crown British monarchs. No mention of opals. Here we can see (I think I have it right) - on the band, 3 green tourmalines, yes 3, which includes the central gem (unless something has been changed since 1998) - on the right arm of the cross, 1 green tourmaline between 2 paler gems probably aquamarines
Edit: source Blair, Claude (ed) 1998 The Crown Jewels - The History of the Coronation Regalia in the Jewel House of the Tower of London, 2 vols, London: The Stationery Office [Blair (ed) 1998]