Simple:
* The farmer's hands were callused from years of hard work.
* The pianist's fingers were callused from hours of practice.
Descriptive:
* Her callused fingers gently stroked the baby's cheek, a stark contrast to the rough texture of her hands.
* The callused soles of his feet were testament to the miles he had walked.
Figurative:
* His heart had become callused after years of heartbreak.
* She built up a callus around her emotions, refusing to let anyone in.
Specific:
* The callused fingertips of the artisan were a testament to his skill and dedication.
* The climber's callused hands gripped the rock face with unwavering strength.