Pertrified Wood slab

Petrified wood occurs when woody stems of plants are buried in wet sediments saturated with dissolved minerals. Because the organisms that break down the wood tissue need oxygen, the decay is slowed down, allowing those minerals to replace the organic material.
Volcanic ash is particularly suitable for the preservation of wood, because the weathering of the ash releases large amounts of silicic acid. But also in sediments that are formed by weathering of igneous or metamorphic rocks, wood can petrify because these sediments are rich in feldspar and other minerals that release silica as they break down.
Silicification begins as quartz binds to the cell walls of the wood. Then the spaces within and between the cells are gradually filled until almost all the organic material has disappeared. Petrified wood contains only 10% organic material, the rest is almost pure quartz.
Most of the colour in petrified wood comes from trace metals. Of these, iron is the most important. Depending on its oxidation state, iron has different shades, from red to yellow. But other metals can also colour petrified wood. Copper, chromium and cobalt can give it a green or blue colour, manganese can make it pink or orange, and carbon and manganese makes it black.
Ever since woody plants first appeared on dry land, in the Devonian, about 390 million years ago, petrification of wood has taken place. Petrified wood is therefore found all over the world. Sometimes you can even find petrified forests in which the trees have remained in their growth position.
But mostly the “forests” you find are accumulations of driftwood in fluvial environments.