There is only one file type that uses the .MCZ extension:
Compressed Poser Material File
Compressed material information file used by Poser's rendering engine; contains textures that can be applied to 3D models created with Poser; accessible only from the Library within the Material Room.
Uncompressed Poser material files use either a .MC5 or .MC6 extension.
NOTE: Poser was originally developed by Smith Micro, but was sold to Bondware in June 2019.
Updated: June 7, 2020