I opened up a wall in a house that looks to have been built in the late 50's or early 60's that was moved to a different location in 1972 due to the Atlanta Airport expansion. It had a loose material in the wall that all poured out when the hole was cut. Who knows what material that might be? I assumed it was poured into the outside wall cavitys before being re bricked. Thanks

Cellulose is light and sort of a beige color, and looks like cotton, and is a natural plant product.
Rock wool or mineral wool (basically the precursor to fiberglass) is whitish grey usually, and many times heavier, and you can see tiny glass pieces about 1/16" long dripping down if you pick it up. They spun it some, but not as much as later spun glass, that has a plastic base and is much lighter.
Those are the two guesses I have.

Some older houses had vermiculite, an expanded mineral. Looks like shiny granules that are bb size or less. It was a pouring insulation that was used to insulate after the siding was installed.