C++ / openGL: Rotating a QUAD toward a point using quaternions

You may have already found this - http://gpwiki.org/index.php/OpenGL:Tutorials:Using_Quaternions_to_represent_rotation - but I found it useful when I last looked into this topic.

Rotation axis = normalize(crossproduct(currentNormal, desiredNormal))

Rotation angle = acos(dotproduct(normalize(currentNormal), normalize(desiredNormal)).

You can build either rotation matrix or quaternion from axis and angle. Exact formula can be found in any resource about quaternions.

You may need to flip angle or axis depending on whether you rotate normal around its' base or around its' tip.

Also THIS resource seems to have enough information about quaternions, rotations, and 3d space in general.