Iodine is a metalloid. Metalloid elements have one or more allotropes with properties intermediate between those of a metal and a nonmetal. Metals are lustrous, ductile, and conductive of heat and electricity. Metalloids may be semiconductors , like silicon, germanium, arsenic, and carbon (graphite). They may be lustrous, but brittle, like iodine and tellurium. Photography was the first commercial use for iodine after Louis Daguerre, in 1839, invented a technique for producing images on a piece of metal.