Geology Word of the Week: F is for Fumarole

Fumarole 1. Yellowstone, Western USA, Fall 2005.

def. Fumarole:
A crustal opening, usually in the vicinity of a volcano, through which steam and other hot gases-- such as carbon dioxide, sulfur dioxide, and hydrogen sulfide-- are emitted. Fumarole comes from the Latin word "fumus," which means smoke. According to the Oxford English Dictionary, the word was incorporated into English through the French word "fumarolle" [1].

Geology Word of the Week: E is for Eclogite

Eclogite from the Mariánské Lázně Complex in the west Czech Republic.
Keele collection. Check out those gorgeous pink garnets!
Photo courtesy of Ian Stimpson.

def. Eclogite:
A high-pressure, high-temperature, coarse-grained metamorphic rock consisting primarily of pink-red garnet (almadine-pyrope variety) and green pyroxene (omphacite, a sodium-rich variety). Eclogites may also contain small amounts of other high-pressure minerals such as kyanite, quartz, hornblende, and zoisite. Eclogites form when mafic rock (basalt or gabbro) descends deep within the Earth, generally at a subduction zone. Mafic rocks consist primarily of pyroxene and plagioclase (along with some amphibole and olivine). At high pressures and temperatures, the original minerals in mafic rock are squished into the more compact (denser) minerals garnet and omphacite, and the mafic rock becomes eclogite. Eclogites form when mafic rock encounters temperatures greater than ~400 degrees Celsius and pressures greater than ~12 kbar (or ~1.2 GPa). These temperatures and pressures mean that eclogites form at a minimum depth of ~40 km; some eclogites may form as deep as ~150 km. As a reference, ocean crust (which is comprised primarily of basalt and gabbro) is generally only 6-10 km thick. Because they are very dense and inclined to descend even deeper into Earth's mantle, eclogites are rarely brought to Earth's surface. Eclogites may be exposed in ophiolite sequences and other places where deep mantle rocks are brought to Earth's surface. Often, eclogites experience partial or full retrograde metamorphism as they are brought to Earth's surface. That is, if eclogites are brought to the surface slowly, their minerals may change back into minerals that are stable at lower temperatures and pressures. Sometimes, higher-pressure minerals will have rims of lower-pressure minerals around them.

Accretionary Wedge #35: Favorite Geology Words

As many of you know, I hosted the Accretionary Wedge Geoblog Carnival for June, and I asked What's Your Favorite Geology Word? Turns out, many of you have favorite geology words! Geologists-- like many scientists, I suppose-- are fond of their jargon. Personally, I'm so fond of jargon that I blog about a geology word every week. I love many geology words, but if I had to pick an absolute favorite, it's ophiolite.

Thanks so much to everyone who participated and shared a favorite geology word! The words are listed below, in the order in which they were posted. If I somehow missed your word, please let me know in the comments, and I'll add it.

Geology Word of the Week: D is for Delta

The Nile Delta as seen from Earth orbit. Photo courtesy of
NASA and taken from Wikipedia here.

def. Delta:
1. The fourth letter of the Greek alphabet (uppercase Δ, lowercase δ).
2. A popular US airline with questionable service (except for those delicious little snacks they serve with your drink), often-delayed flights, and a hilarious in-flight safety video. 
3. A triangle-shaped deposit of sediment that forms where a river or stream flows into an ocean, lake, or other large, standing body of water.

Geology Word of the Week: C is for Coquina

Coquina rock. Image taken from wikipedia here.

def. Coquina ("co-keen-ah"):
A sedimentary rock consisting of loosely-consolidated fragments of shells and/or coral. The matrix or "cement" consolidating the fragments is generally calcium carbonate or phosphate. Coquina is a soft, white rock which is often used as a building stone. Coquina forms in near-shore environments, such as marine reefs. According to the Oxford English Dictionary, coquina is a loanword from Spanish meaning "shell-fish" or "cockle" (a type of bivalve mollusc). Also according to the Oxford English Dictionary, the word was first used in English (to refer to the building stone) in 1837 in the book The Territory of Florida by J.L. Williams.

Geology Word of the Week: B is for Brunton

Brunton "Pocket Transit" Compass. Image taken from here.

def. Brunton:
A fancy, highly-precise compass used by geologists (and surveyors, engineers, archaeologists, etc.) for navigation and also to measure the strike and dip of rock layers in the field.

Geology Word of the Week: A is for Accretionary Wedge

Illustration of a convergent plate boundary. I've added a red arrow pointing out the
location of the accretionary wedge. Illustration from TASA graphics and taken from here.
Click to view larger.

def. Accretionary Wedge (aka Accretionary Prism, Subduction Complex):
A wedge- or prism-shaped mass of sediments and rock fragments which has accumulated where a downgoing oceanic plate meets an overriding plate (either oceanic or continental) at a subduction zone. The sediment is generally marine sediment that has been scraped off of the downgoing plate by the overriding plate. However, sediment from the overriding plate can also contribute to the accretionary wedge. Fragments of rock from the colliding tectonic plates can also accumulate in an accretionary wedge.  The sedimentary rocks which form at accretionary wedges are deformed, faulted, poorly-sorted mixtures which are often referred to as "melange" (which means "mixture" in French).

Accretionary Wedge #35: What's Your Favorite Geology Word?

I'm hosting this month's Accretionary Wedge Geoblog Carnival here at Georneys. Since I write about a geology word every week (see the "Geology Word of the Week" tag on the sidebar or the post "A Geologist's Alphabet"), I thought it would be fitting to host an etymological Accretionary Wedge. This month's Accretionary Wedge is easy-- if you want you can post just a single word!

The theme for this month is:

What's your favorite geology word?

You can post just the word if you want. You can also add anything you want-- a definition, some pictures related to the word, a story about the word, a poem, a drawing. Anything at all!

I must warn you, though: if you post about a good word, I may use the word in a future Geology Word of the Week post!

To join the geoblog carnival, just write a post on your blog and then link to it in a comment below or in a comment over at the Accretionary Wedge site. If you don't have a blog, you should start one. If you don't want to start a blog, just type your word in a comment below. Please submit your entries by the 26th or thereabouts so that I can compile them by the end of the month. Happy blogging!

Finally, be sure to check out last month's Accretionary Wedge #34: Weird Geology.

A Geologist's Alphabet

Every week (except for the month when I interviewed my dad about Fukushima) since I started this blog back in November 2010 I've posted a "Geology Word of the Week." For some reason I decided it would be fun to cycle through the alphabet from A to Z, and I've now accomplished that, writing about words from Alluvium to Zanclean.

Perhaps the alphabet theme is cliche, but I'm having fun with it. So, I think I'll cycle through the alphabet at least one more time. You can expect another A word (Allochthonous? Alvin? Albite? You'll have to stay tuned!) next week.

Here's my first geologist's alphabet:

A is for Alluvium
B is for (Volcanic) Bomb
C is for Coprolite
D is for Dredge
E is for Eustasy
F is for Fabric
G is for Gondwana
H is for Hotspot
I is for Ichnite
J is for Jurassic
K is for Komatiite
L is for Lithosphere
M is for Magma
N is for Nabkha
O is for Ophiolite
P is for Peridot
Q is for Quaternary
R is for Rock
S is for Speleothem
T is for Travertine
U is for Uraninite
V is for Vesicle (and Vug)
W is for Wadi
X is for Xenolith
Y is for Yardang
Z is for Zanclean

Geology Word of the Week: Z is for Zanclean

 Note: This is a modified version of a post that originally appeared on Skepchick in 2010.

Geologic Timescale Spiral. Image courtesy of USGS. Taken from Wikipedia here. Click to enlarge.

def. Zanclean:
A geologic Age spanning from ~5.33 million years ago to ~3.60 million years ago in the Pliocene Epoch.

Geology Word of the Week: Y is for Yardang

Yardangs 1. Photo courtesy of Michael Welland.

Cross-posted at Through the Sandglass. 

def. Yardang (also sometimes: jardang):
An elongated erosional landform, commonly found in deserts, resembling the hull of an inverted boat. Similar to sand dunes, yardangs typically have a tall, steep side facing the prevailing wind direction and slope gently down away from the wind. Yardangs are formed when looser material is eroded away (primarily by the wind and particle abrasion), leaving behind more consolidated material that is then sculpted into strange, ship-like shapes by further erosion. Yardangs most commonly form in soft rocks such as siltstone and sandstone (rocks commonly found in deserts) but can also form in harder rocks in places where the wind is the primary erosional force. The word yardang is of Turkish origin coming from the word "yar" which means "steep bank or precipice." According to the Oxford English Dictionary, the word yardang was first introduced to the English language in 1904 by the Swedish explorer Sven Anders Hendin.

Geology Word of the Week: X is for Xenolith

Mafic xenolith, Ontario, Canada, 2002. Photo Credit: Ron Schott.

Note: Sorry for the re-post. This post was lost and then mangled somewhat in the blogger mishap last week. I managed to correct the post, but I had to re-post it under a new day and time.   

def. Xenolith:
A foreign rock inclusion, usually in an igeneous rock.

Geology Word of the Week: W is for Wadi (وادي‎ )

A Wadi, Oman, January 2009.

def. Wadi ( وادي): ‎
1. An Arabic word meaning "valley."
2. A valley or canyon-- usually in an arid part of the world such as the Middle East-- that contains an ephemeral streambed, which generally fills with water only after heavy rainfall.

Geology Word of the Week: V is for Vesicle (and Vug)

Vesicles in basalt, image courtesy of Ron Schott of the Geology Home Companion Blog.

def. Vesicle:
A small cavity in a volcanic rock that was formed by the expansion of a bubble of gas that was trapped inside the lava.

Geology Word of the Week: U is for Uraninite

Botryoidal uraninite. Image taken from wikipedia commons here.

def. Uraninite:
A uranium-rich mineral with the formula UO2 (uranium oxide). Often, part of the uraninite is oxidized with the formula UO3. Uraninite is the primary ore for uranium and can also be mined for other elements such as radium, thorium, and lead, which are decay products of radioactive uranium. Uraninite deposits are generally a dark steel black with a slight metallic luster. The shape of uraninite is typically botryoidal (looks like a bunch of grapes) or amorphous, but rare cubic and octahedral crystals can form in certain environments. Uraninite often forms when hydrothermal circulation picks up uranium from a uranium-rich rock (such as granite or syenite) and concentrates this uranium in a hydrothermal ore deposit. The primary reason that uraninite is mined is to provide fuel for nuclear power plants.

Geology Word of the Week: T is for Travertine

Travertine terraces, Yellowstone, Western USA, Fall 2005.

After a month's absence because of the Fukushima interviews, I am resuming the geology word of the week. For my new readers, every week I blog about a geology word. Over the past several months, I have been working my way through the alphabet, from A is for Alluvium to S is for Speleothem. I hope you enjoy this weekly feature!

def. Travertine:
1. Formal and specific: "A chemically-precipitated continental limestone formed around seepages, springs, and along streams and rivers, occasionally in lakes and consisting of calcite or aragonite, of low to moderate intercrystalline porosity and often high mouldic or framework porosity within a vadose or occasionally shallow phreatic environment. Precipitation results primarily through the transfer (evasion or invasion) of carbon dioxide from or to a groundwater source leading to calcium carbonate supersaturation, with nucleation/growth occurring upon a submerged surface (Pentecost, 2005)."

2. Translation of the above + a little more: A type of limestone (a calcium-rich rock composed primarily of the CaCO3 minerals calcite and aragonite) which forms by chemical precipitation (the stuff that makes the rock falls out of solution) from certain types of shallow or surface waters, such as springs and rivers. The trigger for the precipitation is usually gain or loss of carbon dioxide (CO2), which causes a pH change and changes the solution chemistry so that CaCO3 precipitates. This gain or loss of CO2 usually happens very close to the Earth's surface as the CO2 is lost to or gained from the atmosphere. The waters that produce travertines are usually very acidic (low pH) or very alkaline (high pH). Often, travertines precipitate from acidic hotsprings, such as those at Yellowstone in the Western USA. However, contrary to many web sources (this wikipedia article, for instance), travertines do not always form at hotsprings; they can also form from cooler waters. Closely related to the word travertine is another T word: tufa. The difference between travertine and tufa is porosity-- tufa is a type of highly porous travertine that generally forms from cooler waters (not hotsprings).

Geology Word of the Week: S is for Speleothem

Before I started a geology blog, I used to sporadically blog about geology over at Skepchick. These days, I blog here at Georneys about geology, and I blog over at Skepchick about other skeptical and scientific things, such as how to spend your final days before an apocalypse. Occasionally, I will re-post some of my old geology posts from Skepchick. I will also sometimes cross-post on both blogs. The post below originally appeared on Skepchick in 2009 here. I have modified and added to the original Skepchick post.

Posing with a pseudostalagmite, Oman, January 2009.

def. Speleothem:
An encompassing term used to describe all types of chemical precipitates that form in caves.

Geology Word of the Week: R is for Rock

"In spite of the difficulty in defining rocks, most rocks are easily recognized when you see them, and most are made of minerals or mineral-like substances. They are usually solid, hard, and heavy, compared to the other materials you see and use daily."
-From Rocks and How They Were Formed by, Herbert Zim, Golden Library of Science, 1961.

Carbonate rocks, peridotite rocks, mountains, and field vehicles, Oman, January 2010.

def. Rock:
1. A solid mass of matter-- usually composed of one or more minerals or mineraloids-- that occurs naturally on the Earth or another planet or extraterrestrial body.
2. What geologists study.

Geology Word of the Week: Q is for Quaternary

Quaternary Girl. Base image taken from here.

def. Quaternary:
The most recent Period of geologic time. We have been in the Quaternary Period for the past ~2.6 million years. The Quaternary Period is located within the Cenozoic Era and is further sub-divided into the Pleistocene and Holocene Epochs.

Geology Word of the Week: P is for Peridot

Before I started a geology blog, I used to sporadically blog about geology over at Skepchick. These days, I blog here at Georneys about geology, and I blog over at Skepchick about other skeptical and scientific things, such as the elusive tree octopus. Occasionally, I will re-post some of my old geology posts from Skepchick. I will also sometimes cross-post on both blogs. The post below originally appeared on Skepchick in 2009 here. I thought I would re-post this because, if you haven't figured it out already, peridotite is my favorite rock and peridot is my favorite gemstone. If you want to learn more about where peridotite (and some peridot gems) come from, be sure to read last week's geology word O is for Ophiolite. After this, I will try not to write about peridotite and peridot for awhile-- though no promises since they are my favorite rock and gemstone.

Peridot gemstone. Image taken from here.

def. Peridot:
Peridot is a gem-quality olivine [(Mg,Fe)₂SiO₄], a beautiful green mineral found in mafic to ultramafic rocks.