A natural yellow earth mineral primarily composed of goethite (iron hydroxide) and clay. Yellow ochres occur naturally throughout the world and have been used as a pigment since prehistoric times. Synthetically produced yellow ochre pigment, introduced at the end of the 18th century, is sold under the name of Mars yellow. Synonyms: goethite; yellow ochre; Mars yellow. Museum of Fine Arts, Boston (2000). [J. Cassar, R. de Angelis]