The process of fossilization can vary according to the type of tissue and external conditions. The most common method of fossilization is called permineralization, or petrification. After an organism’s soft tissues decay in sediment, the hard parts — particularly the bones — are left behind. Water seeps into the bones and minerals dissolved in the water crystallize within the spaces within the bone. Over time, these crystals fill in the spaces and harden into rock³.
Different ways of fossilization are present. For instance permineralization, it is the process by which fossilisation occurs when an organism is buried. In this case, the empty spaces found inside an organism get filled with mineral-rich groundwater¹.