For the curious, I'm playing a Folkcraft chromatic mountain dulcimer on this tune, which has some neat twists and turns.
Rob Thomas' "Her Diamonds" was recorded in the key of G, which for me is singable, but I wanted to get it down into a more comfortable range, thusly F.
The verse moves through these three chords:
F - G7/F - Bbm/F
returning to the F as a bridge between verses. The voicing of the G7 and Bbm (with the F as the root) makes less of a lateral jump and keeps the progression tense and mysterious. Of course, what do these three chords have in common?
F = F* - A = C
G7 = G - B - D - F*
Bbm = Bb - Db - F*
Normally, the F would shoot from the root to the dominant 7th and then hang out as the perfect fifth - but with the above voicings, it remains put at the root of all three chords. Pretty cool, huh?
Onto the chorus:
F - C - Gm - Bb (repeated twice)
Another thing that's neat about this tune is how it changes character, using some of the same chord roots, from dark and eerie in the verse to light and somewhat uplifting in the chorus. Notice that our bright and shiny G7 is now a dark Gm and our previously chilling Bbm is now a major lift of Bb. For more flavor, you could change the C to a C/E and feature a walk-down of the bass in transition from C to F.
And the bridge:
Bbm - F - Bbm - F - Dm - G - Bbm - F
Basically sets up between the first and third chords of the verse, re-establishing a connection with the initial groundwork of the tune, then introduces a new chord to the entire mix, the Dm, which lifts to a positive-sounding G (right at the point where the lyric "she'll be alright" appears for the first time) before settling back into the haunting chord pairing.
Rob Thomas is a brilliant songwriter and I would love to get inside of his head during the process - this tune in particular has no wasted space; every placement of notes has a purpose, from melody to arrangement. I love digging into these tunes as they come my way, hoping that you'll get something out of the process too. Enjoy!