The invention refers to an injectable composition for a bone mineral substitute material, which comprises a dry powder mixed with an aqueous liquid. The powder comprises a first reaction component comprising a calcium sulphate hemihydrate with the capability of being hardened to calcium sulphate dihydrate when reacting with said aqueous liquid; a second reaction component, which comprise a calcium phosphate with the capability of being hardened to a calcium phosphate cement when reacting with said aqueous liquid; and at least one accelerator for the reaction of said first and/or second reaction component with said aqueous liquid. A method of producing an injectable bone mineral substitute material is also provided, wherein the composition is mixed in a closed mixing and delivery system for delivery.