Martensite, named after the German
Adolf Martens (1850–1914), most commonly refers to a very
hard form of steel crystalline structure, but it can also refer to any crystal structure that is formed by
diffusionless transformation. It includes a class of hard minerals occurring as lath- or plate-shaped
crystal grains. When viewed in cross section, the
lenticular (lens-shaped) crystal grains are sometimes incorrectly described as
acicular (needle-shaped).