A vocabulary of landscape — a landscape of words
1469 entries
geode
A geode is a rounded rock with a hollow inside lined with crystals. From outside, it is a plain lumpy nodule. It forms when a cavity in rock, left by a gas bubble in lava or by a dissolved-out shell or root, slowly fills from the walls inward with mineral carried in by groundwater, and the crystals grow into the empty space rather than being squeezed by it, which is why they come out well formed.
Etymology
The word is Greek for earthlike, and it was used by Pliny for a stone that appeared to have earth inside it. What he meant by that is not entirely clear, but the name stuck to the hollow nodule. The word is built on the same Greek root behind geology, geography, and geo, which is a coincidence of spelling rather than a family relationship in the Norse case.
Notes
If the cavity fills solid rather than staying hollow it is a nodule rather than a geode, and the distinction is only knowable by cutting. The Pulpí Geode in Spain is large enough to walk into, about thirty feet long, lined with clear gypsum crystals up to six feet. Most geodes are the size of a fist and are found by weight, since a hollow one is lighter than it looks.