In select situations after an organism dies, mineral water floods the cells of a tissue and leaves crystalline deposits. As the water dehydrates over time, the tissue is preserved in a high-detail cast, creating a fossil. In this micrograph, dinosaur bone was fossilized by water that deposited microscopic quartz crystals, turning the space between cellular structures to agate. Agatized dinosaur bone allows scientists to study ancient organisms at the cellular level because the process prevents tissue distortion while also revealing information about the environment in which the organism lived.
A core of amethyst (purple quartz coloured by iron) and an outer layer of white agate have filled in the marrow cavity in the centre of a thin slice of backlit dinosaur bone from the Smithsonian’s National gem Collection. Further white agate has replaced the cellular structure of the bone around the cavity, showing us its internal workings.