If Andy is dismantling or removing your Aga and it’s old then it could be insulated with Kieselguhr rather than the more ‘modern’ vermiculite.
Kieselguhr was used to insulate Aga’s up until the mid to late 1960’s. It is extremely messy and can sit in the atmosphere for several weeks, it cannot be hoovered effectively and turns back to clay when wet.
If your Aga is insulated with kieselguhr it has to be dug out by hand, all work surfaces, units and appliances have to be protected with plastic sheets as the kiesel will permeate through cotton dust sheets.
If possible it is preferable to remove the Aga in one piece by rolling outside to dismantle.
Showing the mess that is created by this process below..