If you give a gemstone to a chimpanzee, there is very little chance that it will return it to you. This is the lesson learned by a team of Spanish scientists after entrusting different crystals (quartz, calcite, pyrite, etc.) to monkeys collected in a refuge near Madrid, the capital of Spain. The animals became so attached to them that the researchers had to negotiate to get the crystals back for bananas and yogurt – some small stones were never even returned by the chimpanzees.
The study, published on March 4, 2026 in the journal Frontiers in Psychology and relayed by the New York Times, was led by Juan Manuel García-Ruiz, crystallographer at the Donostia International Physics Center, in San Sebastian (Spain). His ambition was to understand why human beings, since prehistoric times, have been fascinated by these brilliant and geometric objects that are crystals, sometimes without any identified practical use.
Archaeological discoveries prove that hominids were already collecting quartz around 700,000 years ago, without using it for their tools or ornaments. Even today, many people say that crystals have therapeutic or spiritual properties. “Some colleagues believe that we should tell people that this belief is completely ridiculous, explains Juan Manuel García-Ruiz. But for me, the important thing is to explain why (it exists).»
To explore the subject, his team worked with two groups of chimpanzees housed at the Rainfer Foundation, a shelter dedicated to these animals located in Madrid. During a first experiment called “The Monolith” – in reference to the film 2001, A Space Odyssey by Stanley Kubrick – the researchers placed a large quartz crystal next to a similarly sized block of sandstone in the enclosures. The monkeys’ reaction was immediate. In one group, a female tore the quartz from its base, which then remained under constant surveillance, while no animal bothered with the sandstone.
Quartz versus food
In a second enclosure, the experiment was cut short because a chimpanzee took the quartz to the monkeys’ dormitory, a place humans avoid going. To recover the stone, the researchers had to carry out food exchanges, proving that primates placed a high value on this mineral.
A second series of tests consisted of scattering a few crystals among pebbles. The chimpanzees sorted the shiny minerals, put them in their mouths, pointed them toward the light, and observed them closely. Cameras installed in the dormitories showed that one of the chimpanzees still had a crystal in his hand before lying down in his straw nest.
For Juan Manuel García-Ruiz, the transparency and geometry of the stones could explain this attraction. He even states a hypothesis: “As the only Euclidean object in nature, the crystal could have contributed to the emergence of geometric thinking in humans.» A postulate that could shed light on our own current attraction to these precious stones.
But other specialists remain doubtful about such announcements. For Michael Haslam, archaeologist at Historic Environment Scotland, in Edinburgh, Scotland, the sample of the experiment was too limited to have any value as proof, especially since these chimpanzees were from rescues, therefore with an atypical background. Juan Manuel García-Ruiz now hopes to repeat the experiment with wild chimpanzees, convinced that the mystery of the crystals is still far from being completely elucidated.
