Obsidian white dating
While pure Obsidian is dark in appearance, the colour varies depending on the presence of impurities.
Also like other glass, Obsidian is metastable at the earth's surface which means that over time the glass becomes fine-grained mineral crystals.
The process can be sped up in the presence of water.
This also means that Obsidian is only found in relatively modern areas, and in none older than the Cretaceous age (from 135 million to 63 million years ago).
However, obsidian hydration can only be used on surfaces which were exposed by flintknapping (the process of chipping and shaping flint to give it sharp edges useful for scraping and cutting) and it is not effective on surfaces that are uneven due to gradual weathering caused by natural forces.
To use obsidian hydration for absolute dating it is important to know the conditions that the sample has been exposed to.