Which mineral property can be observed casually but may mislead identification due to impurities?

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Color is a quick, casual clue you can observe with the naked eye, but it can easily mislead identification because impurities and defects in a mineral can change its color. Even the same mineral can appear in a wide range of hues if trace elements, irradiation, or structural flaws are present. For example, quartz comes in colorless, rose, smoky, and amethyst varieties depending on trace elements and irradiation, while emeralds owe their green color to chromium. Because of these potential changes, color alone isn’t a reliable identifier; it’s best used in combination with more diagnostic properties like hardness, streak, cleavage, and density to correctly identify a mineral.