Iolite was first seen when she and Angel were the first engines to welcome Star and her friends to the railway. She was then seen arguing with Ametrine. Then, Blue Topaz came over to them and told Iolite and Angel that they were needed in the yard. That night, Iolite was seen sleeping next to Star in the sheds.
Bismuth later mentioned Iolite when she said how happy she was that Iolite had introduced her to Mystic Quartz and Mystic Topaz.
Iolite is very kind, but also very stubborn. She is also prone to arguing with those that she does not like, namely Ametrine.
Iolite is based on an LMS Ivatt Class 2MT tank engine developed for the London, Midland and Scottish Railway. Unlike her basis, she lacks a sand dome. Arthur, Amethyst, Citrine, Bloodstone, Domog, Cherry Quartz, Lace Amethyst, Blue Lace Agate, and Anubis are also members of this class. Her original design featured a 4-6-2 wheel arrangement, however, this was changed to the correct wheel arrangement when she was redesigned.
Iolite is painted light purple with dark purple lining. She has dark purple wheels and dome, and a dark purple bufferbeam and footplate. She also has the number 17 on her bunker in dark purple, and her purple gemstone on her side tanks. She also has a dark purple headlamp and taillamp.