The term 'symbol of hardness' can be represented by two different objects: GRANITE and nails. GRANITE is a type of igneous rock that is formed from magma and is known for its strength and durability. Nails are small metal objects that are used to join two pieces of material together, and are also known for their strength and durability. Both GRANITE and nails are symbols of hardness and are often used in construction and other applications where strength and durability are important.