Mark (unit) Mark (unit) The Mark (from Middle High German: Marc, march, brand) is originally a medieval weight or mass unit, which supplanted the pound weight as a precious metals and coinage weight from the 11th century. The Mark is traditionally a half pound weight and was usually divided into 8 ounces or 16 Lot. The significance of the "Cologne Mark" (Kölner Mark) in the German-speaking areas corresponded to about 234 gram. Like the German systems, the French poids de marc weight system considered one "Marc" equal to half-a-pound (8 ounces). Like the pound of 12 troy ounces (373 g), the mark
Refractory metals Refractory metals Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy and engineering. The definition of which elements belong to this group differs. The most common definition includes five elements: two of the fifth period (niobium and molybdenum) and three of the sixth period (tantalum, tungsten, and rhenium). They all share some properties, including a melting point above 2000 °C and high hardness at room temperature. They are chemically inert and have a relatively high density. Their high melting points make powder