It's Sonora. Sonora is either Black, Purple, Very Dark Blue, or I have seen Sonora with cream colored or even caramel bands through it. It can range in colors from Pure shiny Black to Dark Blue. SOmetimes, in the less pure forms, you will see sand particles, quartz inclusions, or even fossiliferous materials.
Although, Sonora is actually a misnomer in itself. KY Hornstone and Sonora both come from the St. Louis Chert formation, and Sonora is just an overcooked or over silicifide Ky Hornstone. It has, however, become accepted in both the Archaeological, Relic Collector, and Flint Knapping community as Sonora.