Some rocks can be identified and sorted by the way they respond to magnets or certain chemicals. Rocks that contain iron respond to magnets.

Rocks that have magnetic properties (e.g., magnetite, lodestone) attract pieces of iron. This writer wonders: if there were an area that held several large magnetite or
lodestone rocks, and people had left trash containing iron on or near them, would those rocks attract the iron, and over the centuries, would the rocks absorb the iron and the pieces of iron would actually become parts of the rocks?

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Limestone and marble react to the vinegar test. (They bubble and make a fizzing sound when vinegar is poured on them.)