Seneca examines a stone beside running water.

When water becomes stone for Seneca

Lucius Annaeus Seneca (c. 4 BCE–65 CE), a Roman philosopher born at Corduba in present-day Spain, devotes the third book of his Natural Questions to the waters of the earth. Among the large questions about the origin and course of rivers there is a short consideration of crystal. How could something that looks so like ice become permanently solid? In Seneca’s explanation the duration of the cold matters more than any single winter day.

A change in small steps

Rain water, which contains very little solid matter, once it is frozen becomes more and more condensed through the persistence of the longer cold until all the air is expelled, and it is compressed to the last degree; then what was once moisture is changed into stone.

– Lucius Annaeus Seneca, Natural Questions, 1910, p. 140.[1]

Seneca starts with rainwater. In his account it contains very little solid substance. He pictures what follows as an increasing condensation. Persistent cold eventually drives out even the air. Between two objects that would look quite different on a collector’s table, a bowl of water and a piece of crystal, the reader can now imagine a sequence of states. At the end of the sequence Seneca gives the material a new name.

What a shared word can suggest

In the same passage Seneca draws attention to Greek usage. The word for crystal can also designate ice. For him that shared name offers a clue to set beside the impression made on the eye. Both substances can look clear and admit light into their interior. Someone holding a piece of rock crystal today is holding quartz. The historical interest of Seneca’s account lies partly in seeing how far a resemblance and an inherited word could lead an ancient investigator looking for a continuous process behind the forms visible to him.