What is "ceylonite"

Ceylanite \Cey"lan*ite\, n. [F., fr. Ceylan Ceylon.] (Min.) A dingy blue, or grayish black, variety of spinel. It is also called pleonaste. [Written also ceylonite.]

Ceylonite (first cited 1793) and pleonaste (first cited 1801) are dingy blue or grey to black varieties of spinel. Ceylonite, named for the island of Ceylon, is a ferroan spinel with Mg:Fe from 3:1 and 1:1, and little or no ferric iron. Pleonaste is named from the Greek for 'abundant,' for its many crystal forms, and is distinguished chemically by low Mg:Fe ratios of approximately 1:3. It is sometimes used as a gemstone.