Rough Granite
Create a new 250 x188 @ 72 dpi graphic and type the letter 'O' in 225 point Arial Black.

Create a new layer and fill it in with white. In the channels palette create a new Channel. It will become alpha 1. Press "D" to reset the foreground and background colors, then choose Filter>Render>Clouds. Click on the RGB thumbnail and switch to the layers palette. Filter>Render>Lighting Effects. Set light to directional. Drag the pointer to the upper left corner. Select Alpha 1.

Go to Image>Adjustments>Hue/Saturation and add some color if you like.

While holding the "Ctrl" button down, click on your original text layer. This will select the outline of you text. Then Select>Inverse and press "Delete".

Add some depth to the letter: Layer>Layer Styles>Drop Shadow and use these settings: Mode: Multiply; Opacity: 100%; Angle: 120; Distance: 3; Spread: 0; Size: 5