Could be anything, probably trash! Any approved caps or pills in the US MUST have identifiable markings of some kind to distinguish what it is. That is the law. I would throw it down the garbage disposal.
I am not a dr. My statements are based on years of experience and related education. Consult with the professional of your choice regarding matters of concern.
It's impossible to >> as it is. Clear capsules is one of the ways >>>>>> powder is traficked on the "to the user" level. Be particularly concerned if the capsule is only <50% full with powder - professionally produced vitamin supplements exist as you describe, but should be filled to the brim. Street >>>>>> usually isn't.
I agree with the orignal reply - garbage disposal.