Marha looked tired and thirsty, but made no complaint, no request for hospitality. She fumbled at her throat and pulled out a wire loop that held a jingling collection of metal chits. "Spice tokens from offworlders. Naib Dhartha sent me out to work the sands, to scrape and collect it to be delivered to his merchant friends in Arrakis City. I have been of marraigeable age for three years, but no Zensunni woman – or man – can take a mate until they have gathered fifty spice tokens. That is how Naib Dhartha measures our service to the tribe."
Brian Herbert and Kevin J. Anderson, Dune: The Machine Crusade (60-61)