I saw a tutorial similar to this on thedesignworld.com and wanted to take it a step further.

Start out with a new file, set your foreground color to white and background color to black. Choose Filter > Render > Clouds. Then choose Filter > Artistic > Plastic Wrap. Use the default settings.

Next choose Filter > Stylize > Glowing Edges

Duplicate the layer, and change the layer mode to color dodge.

Go back to your first layer, and choose Filter > Render> Lens Flare.

You should have something similar to this.

Merge all your layers by choosing Layer > Flatten Image. Then choose Image Adjustments > Hue and Saturation. Change the hue until you get something more magma-like.

Next choose Filter > Distort > Ocean Ripple. Use the default settings.

Take your circular selection too, hold shift, and select the circle-like center of your image. Next choose Filter > Distort > Spherize. Choose a value of 100%

You should have a nice magma-ball going on by now!

Duplicate your layer, and choose Filter > Blur > Radial Blur.

This is going to turn into some light beams. Select some random light beams, as shown below.

Choose Select > Feather and choose a value of 4. Then inverse your selection by choosing Select > Inverse. Delete your selection, you should have something similar to mine.

Next I took the dodge tool and lightened my light beams. just slightly around the edges and towards the center. Here is how mine turned out: