Diamonds are precious stones that can be categorized according to their color and hardness. __41__ . Many variations of color are also found depending on the impurities present. Strongly colored gem diamonds are extremely rare and valuable. When a diamond is set into metal, the metal can affect its color. ___42__. Hardness is the measure of a substance's resistance to being scratched, and only a diamond can scratch another diamond. Diamonds are the hardest substances know.
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