MINERALOGICAL AND GEOCHEMICAL SIGNATURES OF SILICIFIED WOOD FROM THE PETRIFIED FOREST, NEW CAIRO, EGYPT

摘要

Samples of silicified wood from the New Cairo Petrified Forest-evidence of a Paleogene forest also abundant at other sites in Egypt-were analyzed for mineralogy, organic carbon (OC), and loss on ignition (LOI) using X-ray diffraction, optical microscopy, and inductively coupled plasma methods. The OC content ranged from 0.04 to 0.16 wt.% and the LOI from 0.4 to 4.3 wt.%. The samples comprising quartz (78.3-100%) 6 goethite (0.3-17.3%) 6 moganite (2-4.5%) 6 gypsum (2%) 6 calcite (0.5-0.6%) are classified into: (1) Silicified Wood A and (2) Silicified Wood B. The first is petrified with only microgranular quartz and the second with chalcedony 6 cryptocrystalline quartz. The quartz precipitated in tracheids and on cell walls in the samples, while the chalcedony formed in the vessels, veins, and holes. Both silica polymorphs appear to have formed directly from primary solutions, rather than from diagenetic transformation of a silica phase. They most likely have originated from weathering in the area, as there are no other petrological sources of silica in the area.