Beautiful colors and very smooth. What is it?

[jmchandler]

 

[galenrog]

Quartz. Visually, it comes in many forms. The brown colors are likely iron oxides that have leached into the cracks over centuries, or not millennia. In my area, it is common river cobble. In other areas, it is fairly rare.

Time for more coffee.

 

[smokeythecat]

I concur with galenrog.

 

[Back-of-the-boat]

Would look fantastic polished. But it might lose some of the colors.

 

[DDancer]

I gotta wonder if the gold colors are a shimmer effect or just an effect of the camera and lighting. Can you describe it?