Chemistry and Mineralogy of Silicified Wood 
Siliceous petrifactions generally contain more than ninety 
per cent, by weight, of silica. In minor elemental composition, 
they are remarkably uniform. Only iron, aluminum, and the 
more common alkaline earth (Ca, Mg) and alkali (Na, K) metals 
are ordinarily present in amounts greater than a few hun- 
dredths of a per cent. Of these, iron, aluminum, and calcium 
are the most abundant. It is not uncommon for one or more of 
these three metals to be present in amounts in excess of one per 
cent, by weight. Semi-quantitative emission spectroscopic ex- 
amination of more than a dozen silicified woods showed that 
many other elements are normally present in silicified woods in 
trace amounts (below the level of one-hundredth of a per cent). 
In some nonsilicified woods, a relatively scarce element (U, 
Ge, or Se, for example) may sometimes be concentrated to a 
substantial amount. The process of enrichment appears to be 
related to the establishment of organometallic complexes be- 
tween the soluble metal ion in ground water and reactive or- 
ganic species formed from the woody tissue during degrada- 
tion. Lignites have the highest uranium concentration of all 
caustobiolites; germanium is highest in coalified woods of low 
ash content (Manskaya and Drozdova, 1968). 
On examining fifteen silicified woods ranging from the 
Upper Devonian to the past century in age and representing a 
wide variety of wood taxa, boron was found as a trace In only 
four, zinc in only one, and phosphorous was not detected at all. 
These three biogenic elements, along with sulfur which was not 
analyzed for, are the four most enriched elements (relative to 
their abundance tn the lithosphere) in living woods.” This might 
suggest that conditions at the time of petrifaction were suffi- 
ciently low in pH to cause B, Zn, and P to be solubilized as 
acidic species and leached away. Also, the absence of phos- 
phorous might be attributed to microbial mobilization (W. 
Lyford, personal communication). 
In addition to the metal ions, all silicified woods contain 
water, about one per cent or less, and organic matter, remnants 
and derivatives of the original wood substance. There is no 
*The ratios of mean concentrations of biogenic elements in living plants and in 
igneous rocks have been tabulated by Brooks (1972) as follows: B (1.70), S (0.96), Zn 
(0.90), P (0.88), Mn (0.40), Ag (0.25), Ca (0.14), Sr (0.13), Cu (0.13), K (0.12), Ba (0.12), 
and Se (0.10). 
