Amygdule

Part of speech: noun

Definitions

1. A geological term describing a cavity within volcanic rock filled with minerals or crystal deposits
2. This term refers to a pocket in volcanic stones where mineral materials accumulate, often enhancing the rock's structure
3. A cavity in volcanic rock that contains mineral or crystal deposits formed after the rock solidified

Etymology: Amygdule is a diminutive built from the Latin "amygdala," meaning almond, which the Greeks had borrowed as "amygdalē" from an Arabic word for almond, "lawz." The reasoning behind the image is easy to see: a rounded, almond-shaped nut turned out to be a good model for the small, roughly oval gas bubbles that get trapped in lava as it cools, and those bubbles later fill with minerals. The English suffix "-ule" is the key to the form. It comes through French and Latin from the diminutive ending "-ulus," which signals something small, so an amygdule is literally a little almond. Geologists applied the word to the cavities themselves, so the picture is of a tiny almond-shaped hollow, not of the mineral filling inside it.