Phacoliths

Part of speech: noun

Definitions

1. A type of geological structure formed by the accumulation of mineral material around a nucleus, characterized by its distinct layered appearance
2. Geological formations that develop from the precipitation of minerals around a central core, often exhibiting unique structural patterns
3. Structures in geology shaped by the deposition of minerals around a nucleus, known for their layered and sometimes irregular forms

Etymology: The plural here is the form of "phacolith," a term that Alfred Harker, an English geologist, coined in 1909 in his book "The Natural History of Igneous Rocks." He first wrote it as "phacolite," building it from the Greek "phaco-," meaning "lens," and the suffix "-lite" or "-lith," meaning "rock" or "stone." The name fits the object: a phacolith is a lens-shaped body of rock, typically intruded into layered strata, so the Greek root describes its outline before any mineral detail is considered. The "phacolith" and "phacolite" spellings both survive, with "-lith" being the form that matches the Greek "lithos" for stone. Geologists use the plural to talk about many such bodies at once, usually when comparing folds of rock across a region.

Synonyms: rock intrusions, igneous intrusions