To provide a method for producing an expandable mica by which production cost can be reduced.

The method for producing an expandable mica comprises: a mixing step of mixing a powdery mica and a metal alkali substance in a mass ration of 1:1 to 1:20; a heating step of heating the powdery mica and the alkali substance after the mixing to 150-230°C and keeping the temperature for 30 min to diffuse metal ions of the alkali substance into the mica; a cooling/washing step of lowering the temperature of the powdery mica by diluting the powdery mica and the alkali substance after the heating with cold water; a first solid/liquid separation step of separating an alkali solution and the powdery mica solid after the dilution; a neutralization step of neutralizing an alkali substance in the mica by using an acidic solution after dilution with cold water, wherein when the pH of the mica is <7, the mica causes an expansion phenomenon; and a second solid/liquid separation step of obtaining the desired expandable mica by diluting the acidic solution with water and separating the acidic solution and the mica solid after the dilution.

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