put it in one of the 5 gram jars that mineral makeup samples come in (or the ones used as travel jars for pigments). you can easily mail one of those jars in a padded envelope.
sucks your msf broke...but it's nice of you to use it as an opportunity to share the msf wealth!
i also wanted to add: for right now put it in a plastic baggie. if there are any crumbles that come off when you're ready to transfer it to a jar, just transfer the larger chunk and then close the baggie and cut off one of the bottom corners, that will act like a funnel to get the rest of the powder into your jar.
