Overview
- In a head‑to‑head trial, a large quartz crystal drew sustained attention over a similar stone, was carried to the sleeping area, and was only returned in exchange for prized food.
- In sorting tasks, chimpanzees rapidly picked out small quartz, pyrite, and calcite crystals from mixed pebbles, often raising them to eye level to look through them.
- Some individuals sorted pieces by form or gloss, mouth‑carried crystals as if to conceal them, and treated them as valuables during keeper exchanges.
- The research, led by Juan Manuel García‑Ruiz at the Donostia International Physics Center, tested Rainfer Foundation chimpanzees near Madrid and is published in Frontiers in Psychology (DOI: 10.3389/fpsyg.2026.1633599).
- Authors link the behaviors to sensitivity to transparency and geometric regularity with possible deep evolutionary roots, while noting the small, human‑habituated captive sample requires cautious interpretation and further field work.