(Mineral) Composition - Rock Name

It is important to distinguish between the minerals and the rocks. The minerals are found in the 'composition' column. The rocks which are made largely from those minerals are in the 'rock name' column. The difference: minerals have a definite chemical composition. Halite is always NaCl (sodium chloride). Calcite is always CaCO₃ (calcium carbonate). Rocks, on the other hand, may contain all kinds of other 'stuff' mixed together with the main mineral of which it formed. In other words, a mineral is a pure substance, always the same, while a rock is far more variable and often a mix of many things.

If a question asks for a mineral, be sure the answer you give is a mineral.
If a question asks for a chemically formed sedimentary rock, be sure your answer is a rock.

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