If you have two rocks and one contains small amounts of water, it will generally melt at a lower temperature than an otherwise identical dry rock.

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Quizplus · Accepted Answer

This is because the water in the rock will absorb heat energy as it melts, which will slow down the heating of the rest of the rock until all of the water has melted. Once the water has melted, the temperature of the rock will begin to rise again. Therefore, the rock with water will have a lower melting temperature compared to the dry rock.

If You Have Two Rocks and One Contains Small Amounts