what are the odds that the sand from my rock garden is aquarium safe?

[Lindsey]

i recently added some sand to my betta's 5.5 gallon aquarium to give it a more natural look, but i only had 4 pounds of sand to add. i found some replacement sand in my closet from and old zen rock garden and im trying to figure if its safe for the fish. is there any way to test it without harming my fish? ive already pre washed it so its ready to go into the tank