earthstory: Incredible opal When forests are buried by hot volcanic ash their existence is sometimes
earthstory:Incredible opalWhen forests are buried by hot volcanic ash their existence is sometimes preserved through geological history for our joy and wonderment by a process of replacement, whereby silica from the ash is remobilised by mineralising waters and infiltrated into the spaces where the trees used to be before the ash burned them up. Sometimes the process is so perfect that individual cells can be made out in the microscope, or the ridges of the bark. Keep reading -- source link