Martensite, named after the German
metallurgist Adolf Martens, is a class of hard
minerals occurring as lathe- or plate-shaped
crystals. When viewed in cross-section, the crystals appear acicular (needle-shaped), which is how they are sometimes incorrectly described. The crystals are a body-centred cubic (BCC) form of
iron and
carbon, and result from the rapid cooling of
austenite during quenching. In the
1890s, Martens studied samples of different
steels under a
microscope, and found that the hardest steels had a regular crystalline structure. He was the first to explain the cause of the widely differing mechanical properties of steels. Martensitic structures have since been found in many other materials.