Demarco Lamonte Castle (born June 20, 1981), also known as Gemstones, is an American singer, rapper and songwriter from Chicago, Illinois. He is most well known for his affiliation with fellow Chicago artist Lupe Fiasco.
Formerly under the stage name Gemini, Castle began his hip hop career through Lupe Fiasco's Atlantic Records imprint, 1st and 15th Entertainment, where he was set to release his debut album, Troubles of the World, in early 2009. The album has since been delayed indefinitely due to his departure from mainstream hip hop and the discontinuation of 1st and 15th Entertainment. After a brief hiatus, Castle returned to the underground hip hop scene and has since signed to Xist Music as he pursues a career in Christian hip hop. Under his new label, Castle released his debut album, Blind Elephant, in 2015.