How does Nora Roberts use imagery in Immortal in Death?

Imagery:

"Affixed to the bottom of the mattress were two small packs. One was filled with pale blue powder, the other a sealed disc. She tugged both free. Clamping down on the urge to break open the powder she studied the disc. It wasn't labeled, but unlike the others, it had been carefully encased to keep it free of dust."