Martensite, named after the German metallurgist Adolf Martens (1850–1914), is any crystal structure that's formed by displacive transformation, as opposed to much slower diffusive transformations. 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 appear acicular (needle-shaped), which is how they're sometimes incorrectly described. "Martensite" most commonly refers to a very har… (More on Martensite)