noun. A rare blue or light yellow to brown crystalline mineral, the rarest of three forms of titanium dioxide, TiO₂, used as a pigment, especially in paint.

noun. One of the three forms of native titanium dioxid; octahedrite. In color it is indigo-blue, reddish-brown, and yellow; it is usually crystallized in acute, elongated, pyramidal octahedrons.

noun. a blue or brown mineral, a form of titanium dioxide, used as a pigment

"He said claims the ink was too recent because it contained a substance called anatase titanium dioxide could be rejected because medieval maps have been found with the same substance, which probably came from sand used to dry wet ink."

octahedrite