This could absolutely be a headline on The Onion.
This made my eyes roll a bit.
"You have free access to this story. Continue reading with a Times account"
I’m willing to bet they will go after the smooth rocks and it’s about rarity, not crystals.
(an "euhedral" crystal is one with lots of obvious facets, an "anhedral" one is one that's been rounded down into a more pebble shape.)
The study had a harder question: "What properties of crystalline stones attracted them?". The abstract has this answer: "We found that transparency and geometric shape were the two attractors guiding chimpanzees."
Maybe this is scientific proof for the diamond industry.
Why? Crystals are pretty, rocks are not. We clearly prefer shiny colorful things to dull beige things, even if shiny things are abundant.