Refers to something mixed in, often unwanted. Commonly used in the negative form 混じり気のない to mean 'pure' or 'unadulterated'.
This water is delicious with no impurities.
彼の親切は混じり気のないものだ。
His kindness is unadulterated.
不純物 is a more technical term for impurities, often used in scientific or industrial contexts, while 混じり気 is a more everyday word for something mixed in.
Standard kanji spelling for 'mixture' or 'impurity'.
Kana spelling of the second element; common in everyday writing.
Alternate kanji using 雑; less common.
Alternate kanji using 交; less common.
Compound of 混じり (continuative form of 混じる 'to be mixed') + 気 ('feeling, sign'). The exact historical derivation is uncertain, but the word has been used since at least the Edo period.