Iron and nickel are two of the most abundant elements found in the Earth's crust. They are both metals that have been used for centuries in a variety of applications. The ORE of iron and nickel is an important source of these metals, and the crossword solution for this term is ORE, which stands for 'original rock-forming material'. Iron and nickel ORE can be found in many parts of the world, and they are mined for their valuable properties.