Chert occurs in a wide variety of colors. Continuous color gradients exist between white and black or between cream and brown. Green, yellow, orange, and red cherts are also common. The darker colors often result from inclusions of mineral matter and organic matter. Abundant iron oxides in the chert can produce a red color. The name “jasper” is frequently used for these reddish cherts. Abundant organic material can produce gray or black chert. The name “flint” is often used in reference to the darker colors of chert.