This is one of two crowns belonging to the Crown Jewels the queen has worn for official events.
Made with a solid gold frame encrusted with semi-precious stones, it weighs 2.23kg (4.9lbs).
In a filmed interview with BBC (viaYouTube), Queen Elizabeth II spoke about wearing the crown.

Due to its weight, the queen noted that “once you put it on, it stays.
It just remains on.”
Although, she did follow one trick to keep it in place.
Because if you did, your neck would break; [the crown] would fall off."