Island tetrad

The island tetrad is an essentially tempered dyadic chord which under octave reduction consists of three 15/13 intervals followed by a 13/10, which closes on the octave since the island comma, 676/675, is tempered out; in other words a 15/13-15/13-15/13-13/10 chord. It can also be viewed as an island tempered version of 1-15/13-4/3-20/13. Contained within it are a barbados triad, the 1-13/10-3/2 chord, and an island triad, the 1-15/13-4/3 chord, which in another position is the 1-3/2-26/15 chord. Another island chord of interest is a 26/15 over a major triad, 1-5/4-3/2-26/15, 5/4-6/5-15/13-15/13 in terms of intervals.