Here's an assessment of whether each mineral is typically considered pure or impure:
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Pyroxene - Generally considered impure as it refers to a group of silicate minerals, composed of various compositions (e.g., augite, diopside) containing different elements.
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Pyrite - Generally considered pure, as it has a specific chemical composition (FeS₂), although it can contain minor impurities.
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Dioptase - Generally considered pure, as it has a specific chemical formula (CuSiO₄·H₂O), although it can have minor impurities.
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Hematite - Generally considered pure, with its chemical formula (Fe₂O₃), though it can contain some impurities.
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Magnetite - Generally considered pure, as it has a specific chemical composition (Fe₃O₄), but can also contain minor impurities.
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Biotite - Generally considered impure, as it is a member of the mica group and can contain various substitutions in its structure.
In summary, pyrite, dioptase, hematite, and magnetite are typically regarded as more pure minerals, while pyroxene and biotite are considered impure due to variability in their compositions.