A gravel can be broken down into different kinds of substances by physical processes. No chemical reactions are needed to separate different parts of gravel into pure substances. This is because gravel is a(n)

Gravel contains different substances, such as different kinds of rocks and minerals, that can be separated by physical methods without changing them chemically. Because its composition is not uniform throughout, gravel is a heterogeneous mixture, not a homogeneous mixture, element, or compound.

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