These blocks of silicified wood are the remains of mersawa (Anisoptera, family Dipterocarpaceae) trees in Java buried in a volcanic eruption millions of years ago. The volcanic ash preserved the tree trunks while water, containing dissolved silica, slowly seeped through and replaced the wood tissues with silica. After millions of years, every trace of wood has been replaced by silica. Silica is the mineral best known as sand. Pure silica is colourless, but colour is provided by traces of copper, iron and other minerals. Silicified wood is also known as petrified wood or opalized wood. These specimens were shipped from Java and donated to FRIM by Dr Francis Ng, former Deputy Director General of FRIM.