Abstract
Fossil forests have world-wide distribution, commonly preserving mineralized wood that displays vivid hues and complex color patterns. However, the origin of petrified color has received little scientific attention. Color of silicified wood may be influenced by the presence of relict organic matter, but the most significant contribution comes from trace metals. This study reports quantitative analysis of trace metals in 35 silicified wood samples, determined using LA-ICP-MS spectrometry. The most important of these metals is Fe, which can produce a rainbow of hues depending on its abundance and oxidation state. Cr is the dominant colorant for bright green fossil wood from Arizona, USA and Zimbabwe, Africa. Complex color patterns result from the progressive nature of the fossilization process, which causes wood to have varying degrees of permeability during successive episodes of permineralization. These processes include simple diffusion, chromatographic separation, infiltration of groundwater along fractures and void spaces, and oxidation/reduction.
Highlights
In a modern tree, the color is due to the presence of lignin and other organic constituents
For woods that are mineralized with iron pyrite, iron oxide, or copper minerals, the color of the fossil wood is determined by the mineral color
The origin of color involves two phenomena: trace metals that play a role in controlling color of silicified wood, and physical and chemical factors that cause these hues to sometimes be distributed in complex patterns
Summary
The color is due to the presence of lignin and other organic constituents. Cellular features may be preserved in great detail, but the original wood color is lost. For woods that are mineralized with iron pyrite, iron oxide, or copper minerals, the color of the fossil wood is determined by the mineral color. For these specimens, the origin of color involves two phenomena: trace metals that play a role in controlling color of silicified wood, and physical and chemical factors that cause these hues to sometimes be distributed in complex patterns. This study reports on samples of silicified wood that span a broad color spectrum, ranging from vivid primary colors to shades of white, brown, and black. Samples include specimens from two localities that are well-known for producing bright colored specimens: multicolored “rainbow wood”
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