In music a mixed-interval chord is a chord not characterized by one consistent interval. Chords characterized by one consistent interval, or primarily but with alterations, are equal-interval chords. Mixed interval chords "lend themselves particularly" to atonal music since they tend to be dissonant.
Equal-interval chords are often of indeterminate root and mixed-interval chords are also often best characterized by their interval content. "Equal-interval chords are often altered to make them 'impure' as in the case of quartal and quintal chords with tritones, chords based on seconds with varying intervals between the seconds."
^Reisberg, Horace (1975). "The Vertical Dimension in Twentieth Century Music", p.371, Aspects of Twentieth-Century Music, chap. 5, p.362-72. Wittlich, Gary (ed.). Englewood Cliffs, New Jersey: Prentice-Hall. ISBN 0-13-049346-5.