The State Budget and Control Board shall sell and convey, for and on behalf of the State, all such real property, assets and effects belonging to the State as are not in actual public use, such sales to be made from time to time in such manner and upon such terms as it may deem most advantageous to the State. This shall not be construed to authorize the sale by the Board of any property held in trust for a specific purpose by the State or the property of the State in the phosphate rocks or phosphatic deposits in the beds of the navigable streams and waters and marshes of the State.