Color is commonly reddish-brown to yellow.
Used as a natural pigment. An epoch of the early Tertiary period, spanning the time between 33.7 and 23.8 million years ago. The presence or absence of various elements is established by examining the appropriate spectral line of their characteristic wavelengths. Although often providing information about non-written events, such history is subject to the vagaries of human perceptions and mental recall. It is named after a Celtic tribe called the Ordovices.