Ochre is the general name of a group of earth pigments, including: red ochre, yellow ochre, purple ochre, umbra and sienna. The main mineral of ochre is limonite (iron(III) oxide hydroxide). This gives everyone a light yellow color.
Red ochre takes its reddish color from the mineral hematite (Fe2O3), which is an iron oxide.
Yellow ochre is limonite (FeO(OH)-nH2O) and is also called golden ochre.
Purple ochre is identical in chemical elements to red ochre, but slightly different due to the way light diffracts from it due to a slightly larger average particle size.
Brown ochre, goethite (FeO(OH)), is a partially hydrated iron oxide. Amber contains between five and twenty percent manganese, making it a darker brown. Sienna contains limonite and a small amount of manganese oxide, about 5%, which makes it darker than ochre.
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