Droplet of ballpoint ink in water (why)

[Willsr]

I was wondering, a ballpoint pen ink droplet is droped on water, it floats and moves, why?
Is it density, viscosity, surface tension or something else. I am pretty stuck

 

[Doug Huffman]

If it is indeed floating then its density is less than water.

It may be light enough and hydrophobic to not exceed the surface tension that also causes the motion due to variations in the force potentials between the water and the ink - electrostatic is the obvious one.

 

[Danger]

Brownian motion might also contribute.

 

[Meir Achuz]

It could be held up the surface tension of the water. When that happens, the small object on the surface will move back and forth due to slight perturbations of the water surface.