Introduction:
Minerals are naturally occurring inorganic substances that have a definite chemical composition and a crystalline structure. They are the building blocks of rocks and play a crucial role in various industries. Metallic minerals are minerals that contain metal elements, whereas non-metallic minerals do not. In this case, we are asked to identify the non-metallic mineral from the given options.

Explanation:
Let's analyze each option to determine whether it is a metallic or non-metallic mineral:

a) Gold:
Gold is a well-known metallic mineral. It is a dense, soft, and malleable metal with a bright yellow color. Gold is highly valued for its aesthetic appeal and is used in jewelry, electronics, and as a store of value.

b) Bauxite:
Bauxite is also a metallic mineral. It is the primary ore for aluminum, which is a lightweight and highly conductive metal. Bauxite is a reddish-brown rock that is rich in aluminum oxide and is extensively used in the production of aluminum.

c) Limestone:
Limestone is the correct answer and not a metallic mineral. It is a sedimentary rock mainly composed of calcium carbonate. Limestone has a wide range of uses, including as a building material, in the production of cement, and as a flux in the steelmaking process.

d) Iron Ore:
Iron ore is a metallic mineral. It is a rock that contains iron in varying quantities, usually in the form of hematite, magnetite, or siderite. Iron ore is the primary raw material used to produce iron and steel.

Conclusion:
Out of the given options, limestone (option c) is the only non-metallic mineral. Gold, bauxite, and iron ore are all metallic minerals. Understanding the distinction between metallic and non-metallic minerals is important for various industries and their specific applications.