1. Create a new RGB Image of you desired size.

In the channels palette click on new Channel. It will become alpha 1.

2. Press "D" To reset the foreground and background colors. Filter>Render>Clouds

3. This is what you will see in alpha 1. Still in the Channels palette, click on the RGB thumbnail. Switch to the layers palette.

 

 

4. Filter>Render>Lighting effects.

Set light to directional.

Select Alpha 1.

Click ok.

5. Instant rock.

6. Go to Hue/Saturation and add some color if you like.