True about mounting stones is
Fast setting
High expansion
High strength
All of the above
The use of an articulator makes it necessary to mount the casts using a gypsum-producing product. These materials are referred to as "mounting" stones or plasters. They are fast setting and have low setting expansion. The mounting plaster has a sufficiently low strength to permit easy trimming and facilitate separating the cast from the articulator mounting plates.
Phillips Science of Dental Materials ed 12 pg 191