The FBI tests did not identify the substance, but they came back negative for the poison that is extracted from castor beans, said San Antonio FBI spokesman Rene Salinas.
"There were no proteins in there to indicate it was in fact ricin," Salinas said. He said was unlikely further testing would be done.
State health officials did "just a quick test and they don't check for the proteins in ricin," said spokesman Doug McBride.
The mystery powder spilled onto Kelly Heinbaugh's hands as she unwrapped a roll of quarters in her dorm room on Thursday. She said she'd used five other rolls of quarters her mother had gotten from the same bank and none had powder in them.
The 19-year-old freshman and her roommate were both evaluated for possible exposure to ricin and cleared at a hospital.
Roughly 400 residents of the Moore-Hill dormitory were evacuated Friday night while hazardous materials crews sanitized the area where the substance was found.
Salinas said it was unclear whether the FBI would continue its investigation into how the substance ended up with the coins.
If it was put there as a joke, Salinas said "it was an extremely bad joke."