Cesium is the softest metal on Earth. In fact, the metal is so soft, it is possible to cut it with a butter knife. Additionally, cesium melts at a relatively low temperature of 28.4 degrees Celsius (83.12 degrees Fahrenheit). Gold, silver and copper are other malleable metals considered "soft," but they are much harder than cesium.
Discovered by the German chemist Robert Bunsen, namesake of the Bunsen burner, cesium has an atomic number of 55 and is the heaviest of the natural alkali metals. Cesium's name comes from the Latin word "caesius," which means "sky blue." However, this does not reflect the metal's color, which is a pale gold color in its pure form.