Lignite is a type of low metamorphism fossil coal that is a transition form from peat to coal. It differs from peat in terms of its appearance from peat in terms of greater compaction and less discernible vegetation residues, and from stone coals, mainly brown tones. It is also diagnosed by reactions with caustic lye and diluted nitric acid, coloring the solutions into dark brown and bright yellow (up to red brown). In the air is storming and cracking; high hygroscopic and humidity are characteristic. Density 1200-1500 kg/m3.
