n mid-1999 I took an expatriate assignment to Indonesia to work as a geologist in the search for oil and gas. Pretty interesting times—the old dictator who ruled the country for over 30 years was recently removed, and the country was experiencing what could be described as the growing pains of democracy.

What has all this to do with ancient Javanese rainforests and Houston’s art studios? Well it was during this assignment that I began to explore the Java countryside and discovered that it was full of interesting material for the rockhound to collect. But it was one particular type of fossil that caught my eye: Petrified wood. During the next four years or so, I gathered rather a lot. In fact, over 25 tons!

Once prepared, the quality of the best samples is simply stunning, and in my view, is equivalent to or better than the petrified wood from anywhere else in the world. So my great plan was to ship the samples back to my home country (UK) and sell it in my spare time. Things never turn out quite as planned, so no sooner had I shipped a container load back to the UK, my employer decided they wanted me in Houston rather than the UK. So two years ago I arrived in Texas with my family, and naturally I squeezed a few tons of petrified wood into our furniture shipment for “testing” the US market.

Petrified wood in itself is not that rare in Indonesia. This is because in late Tertiary (Pliocene) times, the region experienced near-perfect conditions for the creation of petrified wood. Until man’s recent intervention, the region was blanketed by thick tropical rainforest so there was plenty of wood to start with. These forests often develop on the flanks of volcanoes that occur along the “spine” of the country from Sumatra in the northwest to Bali and beyond in the southeast. It is this close proximity of forests to volcanic activity that was so conducive to preservation of the wood.

Periodically the various volcanoes erupted in much the same way as did Mount St. Helens in 1980. Trees were blown down by the force of the eruption and encased in scorching volcanic ashes. If the trees were too close to the volcano, they were simply incinerated. Too far away, and the trees were not totally covered by the volcanic ash and with time they consequently rotted away in the normal way. However, in the middle of these two extremes, the trees were buried by thick ash which was so hot that it effectively sterilized the trees, destroying all the microbes that normally cause wood to rot.

The volcanic ash has another important function in the generation of petrified wood. It is rich in silica minerals, and the fluids percolating through the ash would also have been saturated with these minerals. The fluids seeping through the ash slowly dissolved the original organic matter of the tree, atom by atom, and replaced it with various silica-rich minerals such as quartz, chalcedony, and jasper. The preservation is so fine that in places you can see the cell structure of the original wood.

The beautiful and varied colors come from trace elements that are dissolved in the silica. Traces of iron, for instance, impart the shades of brown and amber, while manganese oxides produce the blacks and blues. Growth rings are less well developed relative to deciduous trees due to the lack of seasons in a tropical climate, while the large cell structures reflect the moist conditions in which the tree originally grew.

Today petrified wood is found within the volcanic tuffs of western Java in the Pliocene Genteng Formation. Sometimes the samples are exposed within a stream gulley. More often it is still buried and needs to be exhumed with the aid of a pick axe and hard labor in the hot and humid Indonesian climate.

One of the unusual features that characterize petrified wood samples from Indonesia is that the wood is softer than highly silicified material (from Arizona, for example). The Indonesians exploit this feature by using angle grinders (Figure 2) to remove the softer, non-mineralized material and to polish the irregular surfaces, often generating beautiful, abstract shapes in the process (Figure 3). It is these abstractly-shaped pieces of petrified wood that I found so attractive and that now adorn a few of Houston’s art studios.