In the first classification and gradation study on the petrified
wood samples found in the Çamlıdere-Çeltikçi-Güdül fossil forest
of the province of Ankara in Turkey, the samples were firstly divided
into five different representative samples according to their
colourations and specific gravity values. Secondly, they were
grouped into three sub-groups according to their crystallinity
and silica particle size. So, in the toughness and durability gradations,
the petrified woods were graded as tough and resistant
material for first group, semi-tough and semi-resistant material
for second group, and brittle and weak material for third group.