Can You "Handel" This? - The Harmonious Blacksmith by Ted Wolff
I owned a really beautiful vintage Deagan marimba about 10 years ago and recorded a bunch of harpsichord music. The marimba played the right hand part and piano played the left hand part, basically turning solo pieces into duets. Some of them came out sounding pretty good.
This one is by G.F. Handel and is titled, oddly, The Harmonious Blacksmith! It is a theme and variations format, starting with a slow stately melody, and progressively getting a little faster and more difficult with each variation.