Labradorite

“Jon Spiro had not hired Pex and Chips for their debating sills. In the job interview, they had only been set one task. A hundred applicants were handed a walnut and asked to smash it however they could. Only two succeeded. Pex had shouted at the walnut for a few minutes, then flattened it between his giant palms. Chips had opted for a more controversial method. He placed the walnut on the table, grabbed is interviewer by the ponytail, and used the man's forehead to smash the nut. Both men were hired on the spot. They quickly established themselves as Arno Blunt's most reliable leiutenants for in-house work. They were not allowed outside Chicago, as this could involve map reading, something Pex and Chips were not very good at.”
― Eoin Colfer, The Eternity Code