When you get into geology, as opposed to rockhounding, the first thing you need is a dictionary. There are so many different things to keep track of—landforms, minerals, fossils and the parts of fossils—and so many of the words aren't English. Great language though it is, English just isn't up to the task.
First, Go Native
Lots of non-English words stand for geologic things that English speakers never knew about. When European explorers entered new lands, they asked the locals about unfamiliar things. (The story that "kangaroo" actually means "What did you say?" is an old urban legend.)This was not as true with early geologists, because rocks and landforms are pretty universal.
Nevertheless there are still many examples of geology borrowing from native languages. Consider the weird stone hillocks of desert Morocco that the natives call kess-kess. Nothing else in the world is quite like them. Consider the peculiar floodbursts that come from beneath the glaciers of Iceland that the natives call jökulhlaups. The Hawaiian words for smooth and rough lava, aa and pahoehoe, are understood universally. If the natives have a word for it, geologists around the world will use that word.
A Coalescence of Traditions
English speakers were not the only early geologists; most of the European nations have long traditions in Earth science. Indeed, German and French have each had a turn as the default language of geology. So today we acknowledge all Europe as we speak of inselbergs in the desert and echelon fault traces, of lagerstätten in fossil beds and boudinage in the rocks, of chernozems in soils and lapilli in volcanic deposits.
The combined lexicon from the geologists of Europe can be a formidable thing, especially when the languages overlap. The stone most commonly called diatomite may also be called kieselguhr. The erosional opening that cuts through a thrust sheet to reveal the rocks beneath may equally be called a window, a fenster or a fenêtre.
But what if there isn't a word for something because it's never been seen before? Then we recycle two great dead languages, Latin and classical Greek.
The Latin/Greek Connection
It was an accident of history that modern science began with Latin. The cradle of science was in Europe, four or five centuries ago, when the educated classes of every country learned Latin. It was the common language of the Catholic Church and diplomacy and intellectual matters. Isaac Newton described the law of gravity in a book, Principia Mathematica, that was written entirely in Latin. Samuel Johnson, in the 1700s, wrote the first great English dictionary but was just as proud of his Latin poetry. Many people learned classical Greek, too, as a standard part of higher education.
So when geology took its name, two hundred years ago, it was natural for people to plunder the ancient wordbooks when they needed a novel term. And Latin has lots of pieces to build them with—the same with Greek. "Geology" itself is an example: the Greek geo- is earth and -logy is word or discourse—in a word, earth science.
Scientific Latin/Greek is a simplified version of real Latin and Greek. It's very compact, and you can easily build words like ignimbrite. What's that? Well, what would you call a kind of rock that forms when molten lava and ash from an explosive eruption falls in a pile and fuses together into a solid rock? Ignis is fire, imbro- is raincloud, and -ite is stone in scientific Latin/Greek. So ignimbrite is a good label for something that we never had an English (or French or German or Russian or Italian . . .) word for.
Latin Largely Lapses
Latin is still essential today for naming and describing fossils, where features have never been studied before. A neutral name is essential when you can't be really sure what an extinct organism's parts were used for, or where there are nothing to talk about but different doohickeys. Hence we have, for example, the orthotriaene, "a sponge triaene in which the cladi are oriented close to 90 degrees to the rhabdome"—so says the American Geological Institute's Glossary of Geology.
Elsewhere, Latin has slowly lost its hold. For instance, in 1878 a leading geologist could use proper scientific Greek to name the amygdule, but his precise point was lost as many users switched to "amygdale" and its false etymology. It has been roughly half a century since the last major attempt to devise a new latinate word set in geology—that would be the set of names for limestones devised by Robert Folk, which includes terms like "biomicrite" and "pelsparite." Today everyone talks about black smokers, for instance, without trying to give them a shorter Latin name.
PS: And then there are words that have outlived themselves or changed meanings over time. "Geology" itself started out meaning "earth theory," analogous to a cosmology or "universe theory." The word "peneplain" was part of a theory of landscape that has been abandoned. Can we use such a word today without its baggage? And what can we do when the public does to "tectonic" the same thing it did to "quantum"? Geologic terminology isn't all tidy and functional—sometimes it's awkward, even just irritating. What geologic term are you sick of?
