Help with hallmark date on brooch please

[cityofbrighton]

Hello, could somebody help to identify the date markings on my brooch please? It is rather worn towards the bottom end of the mark.

[dragonflywink]

Lovely Scottish Revival piece, believe the stones are a type of quartz called Cairngorm. That's a British design Registry mark, the "I" at the top indicating metalwork, the rubbed bottom letter would designate the manufacturer, the other marks are for the date the design was registered: upper "Q"=1866, left "G"=February, right "23"(?)=23rd day (center "Rd" for registered).

Cheryl ;o)