Petrified Wood from South Africa

This natural mineral has been highly polished on one side only.  It can't really be fully appreciated because of the angle from which the photo was taken. 

The formation of petrified wood began millions of years ago.  When prehistoric trees fell many were covered with sediment or volcanic ash.

Although initially preserved due to being starved of oxygen, some of the organic matter then began to decay.  Any gaps were quickly replaced with minerals being carried in ground water.  As the water dried up they slowly crystallised and hardened.

The process known as petrifaction is sometimes misunderstood.  The crystallised minerals turned to stone not the original organic matter.  The reason why so much detail is often preserved in petrified wood is because the original cell structure often remained largely intact.