Martensite, named after the German Adolf Martens (1850–1914), most commonly refers to a very hard form of steel crystalline structure, but it's also any crystal structure that's formed by displacive 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 appear acicular (needle-shaped), which's how they're sometimes incorrectly described. In the 1890s, Martens studied… (More on Martensite)