Des Moines Fire Department spokesman Brian O'Keefe said Thursday that tests showed the powder was calcium carbonate.
The Iowa Statehouse was locked down for four hours Tuesday after a Democratic lawmaker opened the envelope. It also contained a threatening letter.
Legislative leaders say they want a review of mail-handling and other security procedures at the Statehouse.
House Speaker Kraig Paulsen says lawmakers have never encountered such an incident and should develop procedures in case something similar happens again.
Senate Majority Leader Michael Gronstal says security officials need to be brought into such planning.
