Simple Rock Texture
1. For the purpose of this tutorial open a new document 500 x 500 pixels, transparent background.
2. Go to Filters>Render>Clouds and you should end up with something like this -
Make sure you have the default Foreground and Background colors selected before rendering the clouds by pressing D on your keyboard.
3. To give it it's rock texture we are going to use lighting effects - Filters>Render>Lighting Effects and enter the settings shown below -
Make sure you activate the texture channel by selecting one of the color channels from the drop down box (bottom right), blue works fine for monochrome. Also, ensure the slider is pushed over to mountainous. Hit OK and you will get something like this -
You can move the light source around by dragging on the handles (arrowed).
4. Now to colorize your rock texture, Image>Adjustments>Hue/Saturation and tick the Colorize box. For the purpose of this tutorial just enter the setting's shown below -
Your end result should be something like this -
