The forms of bending in Avatar: The Last Airbender are the classical elements of earth, air, fire and water, and various subsets were revealed as the series progressed. The possibilities are extensive, such as the dark art of bloodbending Katara picks up, and the YA novel The Shadow of Kyoshi has now revealed a hitherto unmentioned form: glassbending.
Kyoshi was the Avatar who lived prior to Aang’s predecessor Roku, a native of the Earth Kingdom whose challenging early life is related in this book and the one it follows, The Rise of Kyoshi. At the beginning of Shadow, Kyoshi is attacked by a street gang in Ba Sing Se, one of whom wields a garrote with ground glass coating its wire. After defeating them, she uses her earthbending to remove the small shards still embedded in her throat, the first (and so far only) time the power has been used on such a material.
The original series already showed sandbending, an earthbending form used by desert tribes that allowed them to shift flurries of loose sand rather than mounds of rock and earth, and as glass is effectively sand subjected to high temperatures, merely an altered state shouldn’t mean that it’s no longer subject to the power earthbenders have over it.
Why no other earthbender has been seen to use the skill is not addressed, but the most likely explanation is that the possibility of it never occurred to them. It wasn’t until Toph was captured and confined to an iron coffin to prevent her from touching the ground to earthbend that she attempted metalbending, achieving it through her enhanced sensitivity from her blindness, attaining advancement through circumstance.
Kyoshi’s primary legacy is the founding of the Kyoshi Warriors, led by Suki when Team Avatar first encounter them, with the art of glassbending seemingly lost with her. However, its mention is another indicator of the vast assortment of possibilities stemming from the abilities portrayed in Avatar: The Last Airbender, and makes you wonder what others are still waiting to be discovered.