The solid purple-black nonmetal that changes to a deep purple gas when heated is iodine.

Here's why:

* Purple-black solid: Iodine exists as a dark, shiny, crystalline solid at room temperature.

* Deep purple gas: When heated, iodine sublimates, meaning it transitions directly from a solid to a gas without becoming a liquid. The gas produced is a deep purple color.

Iodine is a fascinating element with many uses, from disinfectants to photography and thyroid hormone production.