The Latest Verboten Item to take on an Airplane

Not cuticle clippers, not a fountain pen (ink is, after all, a liquid), not pruning shears, not e-coli in a vial or any of the other wonderful and dangerous things you might want to travel with.
It is sand.
I have a charming uncle who collects sand. Perhaps this is because he was born in Alexandria, Egypt, which is perched above the Sahara. Or perhaps this is because he used to dive in the Red Sea. Or perhaps it is because he designs, builds and occasionally travels in submarines. He has sand from deserts and beaches all over the world. And being an engineer, he is extremely well organized and hence his sand is well organized, and labeled. Naturally. His sister (my esteemed mother) brings him back sand from wherever she goes, assuming there is sand there.
So when we were on the coast of El Salvador this past week, walking along the black (volcanic) sand beach, I wanted to bring back some sand for my uncle’s collection. It just so happens that along with gazillions of coconuts in varying states of decay, the beach is also home to more litter than is lovely. We found a littered Gatorade bottle and rinsed it in the warm ocean and then filled it with black sand.

Hopeful, the Ridley turtle, at the beach, heading out to sea

What could be better?
Almost anything not sharp or liquid, it seems. After going through the X-ray machine at San Salvador airport, a security guard looked at my Gatorade bottle full of black sand from many different angles. Finally, I took pity and said, “Es arena. It’s sand.”
“Aha, said he. “That is not allowed.”
“Sand is not allowed?”
“No,” he said, but looked dubious. So he showed my bottle of sand to another security guard (repeat looking at from all angles) who nodded sagely in a negative fashion.
My guard returned and said, “It is not allowed.”
“I can’t bring back sand?” I said.
“No.”
“Why not?”
“You can’t bring in any earth. No puede traer la tierra.”
We all nodded sadly, repacked my suitcase, then CSB and I continued on to gate 6.
But upon later thought I was perplexed. I have brought sand back from Morocco, Tunisia, Costa Rica and New Jersey, and no one has ever objected. Was this a security decision, a customs decision (in which case it wasn’t his to make), or a spontaneous & illogical decision?
Naturally, I go with the last.