Lignite is a variety of coal formed either directly from wood (zyloid lignite) or from compressed plant materials (compact or perfect lignite). When used in jewelry, lignite is more commonly called jet.
Limonite is yellow-orange-brown iron ore commonly used in prehistoric pigments. When ground, limonite produces yellow ochre and darker, earthy tones. Heated, the ore changes partially to hematite, and therefore can also be used to produce red ochres and red-hued browns.