Last summer i flew from SFO-RIX and had some sand from Baker Beach in my bag as a gift for a family member over there. The TSA found it at Security, asked what the hell it was, and then proceeded to take a small part of it out and test it for explosives. After it came back negative, they waived me through no problem.

When they found it in MAN, the security guy was more interested in why i would bring sand as a gift than if it was dangerous or not. As long as you calmly explain what it is it shouldnt be a problem.