What’s in a (geological) name?

Devil's toenail

Devil’s toenail

The Earth Sciences are often about bringing order to the wonderful overflowing complexity of the natural world. The geological way of doing this is often to classify.  A hill-side of rocks, often a bewildering mess to an amateur (or first year student) can with experience be tamed. It can be mapped as a series of rock units, made up of rock types containing minerals. It may contain fossils that can be assigned a species which may reveal which period of geological history it was formed in. All of these things have names. 

Some of these names shed light on the history of the science or the difficulties of classification. Some are poetic, some generate schoolboy sniggers. Let’s meet a few.


Common minerals were first named by non specialists. Quartz comes from an old root word meaning hard, Feldspar is the German for ‘mineral of the field’ and garnet is from an old french word meaning ‘dark red’. However most are named by scientists, after mineral properties, places or people.

Some names are the victim of changing language use. Welsh and Dick are normal names, likewise the town of Cummington doesn’t cause surprise. However the habit of adding -ite to the end of mineral names has created much amusement for students learning the properties of welshite, dickite or cummingtonite.

James B. Thompson, Jr postulated a whole new way of stacking structures in silicate minerals. When examples were found, in his honour they were given the awesome name of  jimthompsonite and even better, clinojimthompsonite: my favourite mineral names.

Dead things

There are manymany fossils and so lots of names. As a student I was powerfully of the opinion that there were too many. My favourite name? Fossil bivalves called Gryphaea have the old popular name of  “Devil’s toenails“.


Let’s start with the Geological Periods:

  • (Pre)Cambrian – latin name for Wales
  • Ordovician & Silurian – latin names for Celtic (Welsh) tribes
  • Devonian – English country of Devon. People from Devon sometimes refer to themselves (correctly) as Devonian, even when they are younger than 400 million years old.
  • Carboniferous – ‘coal-bearing’ in Latin. The industrial revolution was ignited by burning coals from rocks this age
  • Permian – ancient Russian kingdom of Permia
  • Triassic – tri = three. In some areas has three distinct layers
  • Jurassic – Jura mountains, just north of the Alps
  • Cretaceous – Latin for ‘chalk bearing’
  • Tertiary/Quaternary or Palaeogene/Neogene/Quaternary/Anthropocene – lots of Latin

Personally, the whole Latin thing leaves me cold. The names I like best are where another language comes in. Take the original British subdivisions of the Ordovician:  Tremadocian, Arenig, Llanvirn, Llandeilo, Caradoc and Ashgill. These are mostly based on Welsh placenames. Even pronouncing them correctly is a challenge for a non-Welsh speaker.1

The Geological Periods were named by British Victorian gentlemen and reflect their preoccupations (latin, the Romans) and their focus on European geology2. Further subdivisions of time have been changed over the years to better reflect global geology. One major purpose of dividing geological time is to assign ages to rocks. Changing the detailed subdivisions to match specific events (the first appearance of fossil x) makes sense as does naming the new subdivision after areas that contain good sedimentary sequences of this age.

Following this practice, most of the Welsh Ordovician names above have been replaced, by names based on Swedish, Chinese, Australian and American locations. The same applies across the geological timescale. It’s hard not to see this change of names as also tracking the flow of power and scientific innovation around the globe, away from Europe.

Pieces of rock

Rocks mean different things to different people. To a kitchen fitter or an architect, marble and granite are very general terms for hard and soft polishable rocks. Geologists are more precise. Even geologists are precise to a different degree -a rock that might reasonably be mapped as a ‘granite’ might properly be described as a granodiorite.

A type of rock may have a whole series of names. Coal-bearing rocks of Carboniferous age often have a layer of pure quartz sandstone beneath the coal. To geologists an orthoquartzite or arenite this rock was known to miners as a ganister or seatearth, and was used to line furnaces. It formed as an ancient soil horizon so it could also be called a palaeosol.

My favourite rock name is pseudotachylite, which means roughly ‘fake volcanic glass’. It forms when movement along deep fault zones heats rock so much that it melts. It’s other obsolete name is ‘flinty crush rock’ which would be a good name for a musical sub-genre.

Packages of rock

On large scale, geologists identify packages of rock and give them names. Supergroups, groups, formations, units – there are a lot of names for the different types of packages – and countless examples. Packages tend to be named after the place they are best exposed – they have local character.

As a monoglot anglophone (who likes technical terms) I treasure every exposure to non-English words. As a British geologist who had an Irish field area, I’ve heard a lot of gaelic places names, both Scottish and Irish. The Bennabeola Quartzite, the Ariskaig Tillite, the An-t-sron and Ghrudaidh Formations, the Currywongaun Gabbro. Mmmm, close my eyes and I can taste the Guinness (or whisky).

South Africa is a complicated place, with place names based on English, Afrikaans and a variety of African languages. Rock package names pick up this diversity. The ancient Barberton rocks contain the Moodies, Onverwacht and Fig Tree Groups plus the Schoongezicht Formation. The Pongola Supergroup contains the Sinqeni Formation, which contains a Zulu click-sound in the middle that takes a lot of practice to master.

The most poetic set of rock unit names I know come from Yosemite Valley in California. Diorite of North America, Dikes of the Oceans, Tonalite of the Gray Bands – they are the most evocative names for a bunch of granite that I’ve ever heard.

1. The Ll sound is not like the Spanish ‘y’, but is a “voiceless lateral fricative“, don’t ya know.
2. or more correctly their near total ignorance of non-European geology
Categories: History

Comments (1)

  1. Daf says:

    And one of the subdivisions of the Llanvirn (which is an Anglicised spelling ‘cos we don’t have a ‘v’ in the Welsh alphabet) is the distinctly Welsh ‘Abereiddian’. This contains one of the other Welsh letters to cause problems for non-Welsh speakers – ‘dd’.

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