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29 January 2023

Geology Word of the Week: M is for Mica

  def. Mica: A term used to describe a group of minerals that form in flat layers (or sheets) and have a vitreous or pearly luster (they are shiny!). Micas are phyllosilicate minerals, also known as “sheet silicate” minerals. Micas are common rock-forming minerals, although some varieties are harder to find than others. Micas come in many different colors. Common mica minerals include muscovite (clear), biotite (black), and phlogopite (dark brown). …


15 January 2023

Geology Word of the Week: L is for Luster

  def. Luster (or Lustre if you use British spelling): The way in which the surface of a mineral or rock interacts with light. Words used by geologists to describe luster include metallic, sub-metallic, dull (or earthy), vitreous, waxy, silky, greasy, pearly, and adamantine.   Luster is a physical property that is used by geologists to help identify minerals and rocks. Other physical properties that geologists use for identification are …


6 January 2023

Geology Word of the Week: K is for Karst

Several years ago, I used to write a “Geology Word of the Week” post in which I selected a word used by geologists, wrote a definition of the word, and wrote up a post with some information and pictures related to the word. I went through the alphabet in order twice, writing about words starting with letters from A to Z, and then I started a third run through the …


7 January 2015

Geology Word of the Week: I is for Ice

def. Ice: Water (H2O) in a solid state. When naturally occurring, ice is considered a mineral. There are many forms of ice: lake ice, river ice, sea ice, snow, glaciers, ice caps, ice sheets, and frozen ground (such as permafrost).   If you ask a geologist what he or she considers to be Earth’s most important mineral, you will probably hear many different answers, depending on the person. Some might …


1 January 2015

Geology Word of the Week: H is for Hand Lens

I’ve decided to bring back the long-lost “Geology Word of the Week” posts in 2015. For those of you who don’t know, for a few years I regularly posted about a geological word every week. These posts included a brief definition (written by me) of the word and then some additional information and pictures. However, starting in 2012 I stopped posting these words regularly. I was quite busy in 2012 because …


16 December 2012

Geology Word of the Week: G is for Glacial Erratic

def. Glacial Erratic: A rock which has been transported and deposited by a glacier and which has a different lithology than the rock upon which it has been deposited. Often, erratic rocks have an angular shape because they were broken off of bedrock by glaciers and have not yet had time to be weathered and rounded by water, wind, and other erosional forces. Glacial erratics can range in size from very …


9 December 2012

Geology Word of the Week: F is for Float

def. Float: Loose pieces of rock that are not connected to an outcrop. If you’re in the field with a geologist, you’re very likely to hear the word “outcrop” and the phrase “in situ“. When describing, identifying, mapping, and understanding rocks, geologists like to see rocks in context. If rocks were alive, you might say that geologists like to observe rocks in their natural habitats. You might say that geologists …


2 December 2012

Geology Word of the Week: E is for Eurypterid

def. Eurypterid: 1. A group of extinct arthropods that were fearsome marine predators of the Paleozoic. There were over 200 different species of eurypterid, and they ranged from very small (less than 20 cm) to very large (greater than 8 feet). Because of their long tail, eurypterids are sometimes called “sea scorpions.” Indeed, they are closely related to today’s scorpions and other arachnids. One species of eurypterid, Eurypterus remipes, is the …


23 November 2012

Geology Word of the Week: D is for Drumlin

def. Drumlin: An elongated hill or ridge with a shape resembling an upside-down spoon or a half-buried egg that was formed out of glacial till– and sometimes other material such as gravel and even bedrock– that was shaped by the movement of a glacier. A drumlin carved in bedrock is usually called a “rock drumlin.” Drumlins have a steeper end and a less-steep, more tapered end. The shape of a …


18 November 2012

Geology Word of the Week: C is for Columnar Jointing

def. Columnar Jointing: A structure that forms in rocks (most commonly in basalt) that consists of columns (mostly commonly hexagonal in shape) that are separated by joints or fractures in the rock that formed when the rock contracted, most often during cooling. Columnar jointing is always a joy to observe in rocks in the field. Stumbling upon perfectly geometric columns of rock can only be described as magical. Even the …


11 November 2012

A Second Geologist’s Alphabet

I’m already at the letter B of my third geologist’s alphabet, so I thought I should compile a list of my second geologist’s alphabet. During the last year of my PhD, my weekly words were not so weekly. Thus, I blogged my second geologist’s alphabet over the last year and a half or so. My first geologist’s alphabet can be found here. Here’s my second geologist’s alphabet: A is for …


Geology Word of the Week: B is for Botryoidal

def. Botryoidal: Shaped like a bunch of grapes. The word botryoidal comes from the Greek word “botrus”, which literally means a cluster or bunch of grapes. In geology the word botryoidal is often used to describe a rock texture or mineral habit (appearance). Here are a few pictures of some botyroidal rocks and minerals: ***Thanks to Patrick Donohue for suggesting this week’s word and to Patrick and Lockwood DeWitt for …


4 November 2012

Geology Word of the Week: A is for Amygdale

def. Amygdale (also spelled Amygule): Vesicles, generally in extrusive igneous rocks, that are filled with secondary minerals, most commonly quartz, calcite, chlorite, and zeolite. When a rock contains amygdales, geologists often describe it as an amygdaloidal rock. For example, basalt is often described as amygdaloidal basalt. Here are a few previous, related geology words of the week that may be of interest: V is for Vesicle (and Vug) Z is …


28 October 2012

Geology Word of the Week: Z is for Zeolite

def. zeolite: The name of a large group of porous, framework, aluminosilicate (their basic structure is interlocking tetrahedra of SiO4 and AlO4) minerals that contain significant water and also significant exchangeable cations, which makes them absorbent materials. The name zeolite originates from the Greek words “zeo”, which means “to boil”, and “lithos”, which means “stone”. Zeolites were given their name because when you heat them, they generally release water in …


19 October 2012

Geology Word of the Week: Y is for Yellowstone National Park

def. Yellowstone National Park: A United States national park that is located in the states of Wyoming, Montana, and Idaho. Established in 1872, Yellowstone was the first national park to be founded and set an example for other national parks which were subsequently established all over the world. The park is the current location of the Yellowstone hotspot, which is responsible for large-scale volcanism in Oregon, Nevada, Idaho, and Wyoming. …


13 October 2012

Geology Word of the Week: X is for Xiphactinus

def. Xiphactinus: 1. A large (15-20 ft long), predatory fish that lived during the Late Cretaceous. 2. A prehistoric sea monster. Seriously. What an enormous and scary looking fish. 3. A really, really cool fossil. Maybe one day I can display one in the library of my evil geologist lair. One of the most famous fossils of Xiphactinus is the “fish within a fish” fossil located at the Sternberg Museum of Natural …


7 October 2012

Geology Word of the Week: W is for Widmanstätten Pattern

def. Widmanstätten Pattern: An interweaving pattern of the extraterrestrial minerals kamacite (a low nickel content iron-nickel alloy, similar to the terrestrial mineral ferrite) and taenite (a high nickel content iron-nickel alloy, similar to the terrestrial mineral austenite) that appears in some iron-nickel meteorites when a cut section of the meteorite is etched with weak acid. Widmanstätten patterns appear during acid etching because kamacite is more easily dissolved by weak acid than taenite. Widmanstätten patterns are believed to …


26 September 2012

Geology Word of the Week: V is for Vitreous

Introductory Note: At long last, the Geology Word of the Week has returned! For almost a year, the Geology Word of the Week post has been on hold. I briefly resurrected the weekly word back in April with the posts T is for Time and U is for Ulexite, but the revival was short-lived. I neglected the weekly word because this past year has been busy and full of important life events and …


1 May 2012

Monday Geology Picture: Chesterfield Gorge, New Hampshire

This week’s geology picture was taken in the Chesterfield Gorge, which is located just a few minutes from my parents’ house in southern New Hampshire. I would often explore and play at the gorge as a child. I used to like to throw things into the gorge and watch them go over the waterfalls. I once duct-taped a Princess Leia figurine into a plastic toy kayak and watched her go …


28 April 2012

Geology Word of the Week: U is for Ulexite

def. Ulexite: 1. Hydrated sodium calcium borate hydroxide (formula: NaCaB5O6(OH)6•5(H2O) ), a silky, brittle, generally white evaporate mineral  which often crystallizes in the form of densely-packed fibers that transmit light along the long axis of the mineral. 2. A party trick rock. Have any party guests who think that geology isn’t awesome? Just pull out your fibrous ulexite sample and say, “Hey look, I have a fiber optic rock.” Then …