A new crown was made for Queen Adelaide since the previously used crown of Mary of Modena was considered "unfit for Her Majesty's use". The stones used in the crown were removed after the coronation.
Queen Victoria, as a Queen regnant, used a newly created Imperial State Crown.
Queen Alexandra had a new crown created for her coronation, since there as no Queen Consort crown available (Adelaide's having been dismantled). The stones were removed from the crown after use and replaced with paste.
Queen Mary and Queen Elizabeth both had a new crown created for their coronations.
I assume that Queen Mary created a new one because Queen Alexandra was still alive (and she probably wanted her own crown anyway). I'm not sure why Queen Elizabeth didn't re-use Queen Alexandra's (the stones could have been reset).