A mineral-based panel including a mineral-based core and at least one groove. The at least one groove may be provided in a rear side of the panel. The mineral-based panels may be floor panel, a building panel, a wall panel, a ceiling panel or a furniture panel. A method for forming such grooves in a mineral-based panel. Furthermore, a mineral-based panel including a mineral-based core and polymer-based lower layer(s) attached to the core. A locking system of the panel includes a strip extending horizontally beyond an upper portion of the panel, and a horizontal portion of the strip is entirely formed in the polymer-based lower layer(s).