To provide: a hydrous magnesium silicate mineral which is suitably used for a moisture control material improved in the thixotropy during forming, capable of being produced by a short time curing treatment, and having high absorbing and desorbing performances and excellent mechanical properties and composition stability; a composition for a hardened body; an inorganic hardened body; and a carbonated solid.

The composition for a hardened body comprises a hydrous magnesium silicate mineral obtained by firing attapulgite and/or sepiolite at a temperature of 150-800C (preferably, having a median diameter of 5-50 m and contained in an amount of 30-80 wt.%) and a gas-hardenable material and/or a hydraulic material (preferably, calcium silicate having an aspect ratio of 10-25), and (preferably, pulp fiber having a beating degree of 50-200 is incorporated in an amount of 2-10 wt.%). The inorganic hardened body and the carbonated solid are also provided.