Why does anthracite burn with relatively little smoke?

Anthracite burns with relatively little smoke because it contains the lowest amount of volatile matter of any form of coal—typically 14 percent or less on a dry, ash-free basis.1

Volatile matter consists of gases, tars, and low-boiling-point organic compounds that are driven off when coal is heated. In coals with higher volatile content, these substances are released during combustion and can form smoke. Because anthracite is the most highly metamorphosed form of coal, it possesses a very high fixed carbon content (86 percent or greater), meaning most of its mass remains as solid fuel rather than vaporizing into smoke-producing compounds during the heating process.213