www.trade-oracio.com - Petrified wood from Madagascar

In a more technical manner:

The petrification of a plant happens through the infiltration of mineral saturated solutions into the cell structures and into intercellular gaps. This process requires sedimentary matters in solutions or as particles to be available. At the beginning of the petrification process, a large percentage of the original plant’s material remains, enclosed in the mineral matter. As time goes by, the percentage of original vegetal matter replaced by minerals increases, until a total petrification, or chalcedonization is obtained.

For a tree to petrify, it has to be in an anaerobic environment in order to avoid decaying; in other words, it has to be buried in an oxygen free environment, such as a slimy silt rich meander or the bottom of a lake, and that’s the most frequent case with volcanic sediments.

The study of petrified wood forests around the world reveals an indisputable connection with volcanic activity: either as massive ash downpours in the area where petrification took place, as seems to have been the case in northern Arizona, or by the enshrouding of the forest itself under volcanic ashes (that is what apparently happened in Patagonia, Argentina), or else by a forest being engulfed by a lava flow or the related mudflows, as happened in the petrified forest of Oregon and Madagascar.

The basic components of most petrified woods are microcrystalline and hydrated varieties of quartz, generally called chalcedony and opal. Chalcedony can come as agate, or as onyx or sardonyx. Opal is always encountered as common opal: it’s a colloidal silica with a more waxen sheen than chalcedony, it contains more water and doesn’t have the same toughness. The crystalline varieties of quartz, such as amethyst, tinted quartz and citrine can be found at the beginning of large branches or covering the interior of holes in the fossilized wood.

Structure and colorations of the wood :

Petrified wood has a toughness of 5.5 to 7.5 on the Mohs scale (diamond is rated at 10). We are in the presence of a tough and unalterable material, the beauty of which is equaled only by its longevity across the generations.

The many colours that can be observed in petrified wood depend on the chemical composition of the water contained by the soil during the petrification process. The way the tree petrifies, the place where it petrifies, and the compositions of the strata that cover it are as many factors that have an influence over the final colour of the petrified matter. The sediments were essentially composed of ash laden silt, clay and sand. Acidic solutions containing iron and manganese at different degrees of oxidation and reduction gave the petrified woods their multiple rainbow colours. Thus each tree presents a unique array of colorations, depending on its porosity at the moment silica penetrated it.

The colours present in petrified wood and some of the correponding minerals: