Is there a way to have the white areas be clear in this glass marble example?
Use the color output of the color ramp to mix in a Transparent BSDF with another mix shader node. Make sure the transparent BSDF is the bottom slot of the mix shader in this case.
Assign to blue and black on color ramp alpha=0. Make node color ramp alpha into mix shader factor. Change glossy into glass bsdf. For better effect you can add volume scatter/absorption shader. Connect it into volume material output. Hf:)