Vanadium is a metal, and by far its greatest use is in steel

alloys, where tiny amounts of vanadium improve steel’s hardness, toughness, and

wear resistance, especially at extreme temperatures. As I reported in my book

What Things Are Made Of, more than 650 tons of vanadium was alloyed with iron

to make the steel in the Alaska Pipeline, and there’s no good substitute for

vanadium in strong titanium alloys used in jet planes and other aerospace

applications.

Vanadium isn’t exactly one of the well-known elements, but

in terms of abundance in the earth’s crust, most estimates indicate that

there’s more vanadium than copper, lead, or tin. But it’s difficult to isolate,

and it wasn’t produced chemically as a chloride until 1830, when Swedish

chemist Nils Sefström named it for the Norse goddess of beauty, Vanadis,

perhaps better known as Freyja. It wasn’t until 1867 that pure vanadium metal

was isolated by British chemist Henry Roscoe, whose work on vanadium won him

the name of the vanadium mica roscoelite.

As a mineral collector, I’m attracted to vanadinite, lead

vanadate, because it forms beautiful hexagonal crystals, often bright red and

so abundant from one lead-mining area of Morocco that excellent specimens can

be had without mortgaging your house. Some vanadinite crystals are like perfect

little hexagonal barrels, and others can form needle-like spikes around a

central crystal, making the whole thing look like a cactus with caramel-orange

spines.

Some of the vanadium for making steel alloys comes from

primary mined vanadinite, but much more was once produced as a by-product of

phosphorous manufacture, because it’s commonly associated with phosphate rock. And

today, a lot of the world’s vanadium comes from refining crude oil and from fly

ash residues, which are products of coal combustion. I got curious about why

vanadium metal is so closely connected with these organic deposits.

Crude oil actually has lots of trace elements in it,

including metals like gold, tin, and lead, but by far the most abundant are nickel

and vanadium, as much as 200 parts per million nickel and 2000 parts per

million vanadium in some crude oils, especially heavy, tarry oils like those

found in Venezuela. In some oil, the nickel and vanadium can add up to 1% by

weight of the oil, an incredibly huge amount. Refining Venezuelan crude gave

the U.S. a lot of vanadium back in the late 20th century. But why is

it in there?

Oil and coal are both the result of decaying and chemically

changing plant matter. Forget dinosaurs; virtually all oil, natural gas, and

coal comes from plants – usually marine algae for oil and gas and more woody,

land-based vegetation for coal. There’s a class of organic molecules called

porphyrins. I’m no organic chemist, but these complex hydrocarbon molecules, made

of carbon, hydrogen, oxygen, and nitrogen have boxy ring-like structures with

open space in the centers. Chlorophyll and hemoglobin are related chemicals,

both of which contain metals in the middle of the structure, magnesium in

chlorophyll and iron in hemoglobin. The vacant holes in the centers of

porphyrins in crude oil are ideal for trapping metal molecules, and apparently

vanadium, in the form of a VO2 ion, is one of the easiest to trap because of

its molecular size and electronic valence.

The vanadium comes from the original oil source rock, so

there’s quite a range in vanadium content around the world. Heavy oils, like

the tars in Venezuela, hold more than fluid oils like those in Saudi Arabia.

This has more or less been known since at least the 1920s, and today the

vanadium and other metal contents of oils are being used to characterize the

original source rocks even when those source rocks no longer exist or are no

longer what they once were.

The United States has had no mine production of vanadium since

2013 and even then we were 94% dependent on imports. Today 100% of our vanadium

is imported, and we also produce some vanadium from imported crude oil and ash.

More than 90% of the world’s vanadium is mined in China, Russia, and South

Africa, although the US imports much of what it needs from the Czech Republic

and Canada as well as Russia. We also imported enough ash and refining residues

to account for 9000 tons of vanadium in 2015, mostly going as I said to making

steel alloys. A new emerging use is in high-capacity storage batteries, where

vanadium compounds make the electrolyte. These batteries have potential uses

for renewable energies such as wind and solar power, and although in 2015 and

2016 several companies were working on prototype designs, they’re still pretty

expensive batteries.

Way back in 1971 when I was a teaching assistant for the

Indiana University Geologic Field Station, on one mapping project we went to

the Mayflower gold mine south of Whitehall, Montana. I collected a bunch of

rocks with interesting looking sparkly crystals – some of which I’ve only

recently gotten around to really studying. I gave a talk at the 2017 MontanaBureau of Mines and Geology Mineral Symposium on minerals from there that

turned out to be vanadium-bearing, including vanadinite, although it’s probably

an arsenic-rich variety, and stranger minerals like descloizite, a lead-zinc

vanadate, tangeite, calcium-copper vanadate, and some others. I even think

there are some tiny bits of roscoelite, the vanadium mica named for the chemist

who first prepared vanadium metal.  

Even more exciting for me are some tiny, millimeter-sized

red-orange crystals in the specimens I found at the Mayflower Mine. All I knew

for a long time was that I couldn’t figure out what they were. By looking at

their crystal shapes and properties, I narrowed it down to two very strange and

very rare minerals – gottlobite, a calcium-magnesium vanadate, and calderónite, a lead-iron vanadate. Both

of these minerals are so obscure I didn’t really seriously imagine I had

actually collected one of them. But, thanks to an analysis by Stan Korzeb, the

economic geologist at the Montana Bureau of Mines and Geology, it turned out

that I did indeed find calderónite,

32 years before it was described as a new mineral in 2003. Stan’s analysis in

January 2018 used EDX, or energy-dispersive x-ray spectroscopy, a technique

that gives not only the elements present in a mineral, but their relative

proportions, which allowed Stan to calculate the chemical formula. The lead-iron

vanadate calderónite he found is intergrown with

descloizite, a lead-zinc vanadate. This probably indicates changing iron-zinc

concentrations in the fluids that precipitated the minerals. This represents just

the 11th documented calderónite

occurrence in the United States and the second in Montana. Stan identified the

first in Montana in the fall of 2017.

It’s an obscure mineral, and the crystals are tiny, but it

made this mineral collector’s day.

—Richard I. Gibson

Link:

USGS Mineral Commodities - Vanadium (PDF) 

You may have seen some of the spectacular images of the

earth in southern Algeria, curves and colors like some Picasso in the opposite

of his cubist period. If you haven’t, check out the one from NASA, below. 

The ovals and swirls, with their concentric bands, are

immediately obvious to a geologist as patterns of folds, but not just linear

folds like many anticlines and synclines form. These closed ovals represent

domes and basins – imagine a large scale warping, both up and down, in a thick

succession of diverse sedimentary rocks, like sets of nested bowls, some of

them right-side up and some inverted, then all sliced off halfway through.

But “obvious to a geologist” has plenty of limitations in a

space image. Without knowing more information, it’s difficult to be sure if an

oval is a basin or a dome. And you can speculate, but without some ground

truth, it’s challenging to be sure what the rock types are.

Ahnet-Mouydir, Hoggar Mountains, Algeria. NASA image - source

This area, called the Ahnet-Mouydir, on the flank of the Hoggar

Mountains close to the middle of the Sahara Desert, is remote, inhospitable,

and arid, and called the “land of terror” for a reason. The rocks represent a

thick sequence of marine sandstones, shales, and limestones, spanning a huge

range of ages, from at least the Ordovician to the early Carboniferous – 150

million years or more, a great chunk of the Paleozoic era.

The core of the Hoggar Mountains is an old Precambrian

block, not as big as the cratons and shields that form the hearts of most of

the continents, but otherwise similar. It might have been something like a

microcontinent that became amalgamated into the growing supercontinent of

Gondwana about 600 million years ago. After that amalgamation, seas came and

went much like they did in western North America throughout much of the

Paleozoic era, laying down the sediments that became the rocks we see today in

the northern Hoggar Mountains.

That’s all well and good – but here’s the next question, how

did the rocks get deformed into these oval domes and basins? If you imagine the

kinds of collisions that are typical on earth, you think of linear or

curvilinear things – island arcs, edges of continents and such – that when they

collide, are likely to make linear belts of deformation. This is why so many

mountain ranges are long, linear features, and the folds and faults that make

them up also tend to be linear. Domes and basins happen, but that seems to be

almost all we have here in these mountains.

We have to look for a deformational event that is later than

the youngest rocks deformed. So if some of these rocks are as young as early

Carboniferous, about 340 million years old, the mountain-building event that

fills the bill is the Hercynian Orogeny, where ‘orogeny’ just means

mountain-building.

The Hercynian, at about 350 to 280 million years ago,

represents the complex collision between Gondwana and the combined North

America and Europe, which were already more or less attached to each other. The

leading edge of Gondwana that collided was in what is now North and West

Africa, and the collision produced mountain ranges all over – the Alleghenies

in the central Appalachians in North America, and a complex swath of mountains

across central Europe, from Spain, across France to northern Germany and into

Poland, as well as elsewhere. In Africa, the most intense squeezing was at the

leading edge, in what is now Morocco and Mauritania, colliding with North

America, and northern Algeria, impacting Iberia.

The basins and domes of southern Algeria that we’re trying

to understand are 1500 kilometers or more from that leading edge of continental

collision. So I think – and full disclosure, I’ve never really researched this

area in detail – that what must have happened is that that distant hinterland

wasn’t pushed into tight, linear belts like those we find along the lines of

collision, but the force was enough to warp the sediments into these relatively

small domes and basins. Alternatively, it might be possible that the brittle

Precambrian rocks beneath the sedimentary layers broke from the force of the

collision, so that the sedimentary layers draped over the deeper brittle

surface like a carpet lying over a jumble of toy building blocks – some high,

some low.

The latter idea, that the brittle basement rocks were broken

and pushed upward with the sedimentary layers draped over them is supported by

research published in the journal Terra Nova in 2001. Hamid Haddoum and

colleagues studied the orientations of folds and faults in this area, trying to

figure out the orientations of the stresses that caused them. Their data show a

shortening direction – which means compression, or squeezing – during early

Permian time oriented about northeast-southwest. That is consistent with the

collision that was happening at that same time between what is now Senegal and

Mauritania, in westernmost Africa, and the Virginia-Carolinas region of what is

now the United States. Haddoum and his colleagues show cross-sections with

basement upthrusts, basically high-angle reverse faults where older rocks are

squeezed so much that they are pushed up and over younger rocks. This is quite

similar to the Laramide Orogeny in the western United States about 80 to 50

million years ago, but this compression was happening about 280 million years

ago as the supercontinent of Pangaea was assembled during the early Permian

Period. Both represent deformation at relatively great distances from the lines

of continental collision. In the case of the Laramide in western United States,

one idea for transmitting the stress so far from the collision is that the

subducting slab of oceanic crust began to go down at a relatively gentle angle,

even close to horizontal, creating friction and stress further away from the

subduction zone than normal. Whether that’s the case here in southern Algeria

isn’t clear for this Hercynian collision.

I wouldn’t think of this area as high mountains, such as

those that must have formed along the lines of Hercynian collision. Maybe more

like warped, uplifted plateaus – but whatever they were, they were certainly

subject to erosion. Erosion probably wore the domes and basins down to a common

level, so that the nested bowls were exposed in horizontal cross-section –

which for geologists is the equivalent of a geologic map. And that’s what the

beautiful photos reveal.

The area might have been planed off even more by Permian glaciers

during and after the Hercynian mountain-building events. But then, during the

Mesozoic era, seas returned to the region and all this mess of eroded domes and

basins was buried beneath even more sediments. Sometime relatively recently,

during the Cenozoic era, the past 65 million years, everything was uplifted at

least gently, so that the highest parts – including today’s Hoggar Mountains,

were stripped of the younger Mesozoic sedimentary rocks, revealing the much

older Paleozoic rocks in the domes and basins.

—Richard I. Gibson

Link: 

Most of my career was in analyzing features of the earth’s gravity and magnetic fields, to infer geologic structures for oil exploration. But that doesn’t mean I really understand the whole earth’s fields – and for some aspects of it, neither do folks much more knowledgeable than I am. You’ve probably seen the images that show the earth’s magnetic field as like that of a dipole magnet, with north and south poles that don’t coincide exactly with the poles of rotation. That’s fine as a starting point, but in detail, we find that the earth’s field is not smooth and uniform, but it has bumps and changes over time and in space. Today I want to talk about some of the anomalies in magnetic field intensity. At the earth’s surface, the magnetic field varies from about 23,000 to 65,000 nanoteslas, with a tesla being the standard unit of magnetic field strength. It’s not surprising that a body as complex and heterogeneous as the earth would have variations in its physical properties, but a range of 40,000 out of a maximum of 65,000 might seem to be a wide range. The highest highs are over Siberia, northern Canada, and the ocean between Antarctica and Australia, while the one big low is over central South America and the South Atlantic Ocean. That South Atlantic Anomaly has gotten some serious study lately. The weakness of the magnetic field at the South Atlantic Anomaly is enough that increases in radiation – which the magnetic field protects us from – can affect satellites like the Hubble telescope, and the International Space Station has extra shielding just because of the South Atlantic Anomaly. Even at ground level, communications can be disrupted during solar storms. Jay Shah, a student at Imperial College London, studied rocks on the volcanic island Tristan da Cunha, right in the middle of the anomaly, and found that the magnetic field there has probably been weaker than elsewhere on earth for at least 46,000 to as much as 90 thousand years ago, indicating that the South Atlantic Anomaly is probably a fairly persistent feature of the magnetic field. One speculation about the nature of the South Atlantic Anomaly had been that it somehow was an expression of an impending reversal of the magnetic field. We know that these inversions happen, and have happened dozens of times in earth’s geologic past, but we know very little about the actual mechanism of a reversal. The finding that the South Atlantic Anomaly is fairly old doesn’t say it’s not related to a reversal, but it maybe reduces the chances. The evidence suggests that reversals probably happen over a fairly short time span, a few thousand years or even fewer, and probably not a time as long as 50,000 years or more. The earth’s magnetic field is probably generated by electrical currents mostly in the liquid outer core. You can imagine that a fluid, even one as dense and hot and deep as the outer core, would have variations in flow and geometry that would be reflected in the magnetic field generated, and this is almost certainly the case. Models suggest that the South Atlantic Anomaly might be related to some kind of disturbance or variation at the boundary between the outer core and the base of the mantle, but that position is about 2900 kilometers – 1800 miles – beneath the surface. It’s studied mostly by looking at variations in seismic waves, although information about earth’s gravity and magnetic fields also comes from specialized satellites. This is a field of study that’s very much in flux, with new ideas and models coming out yearly. Stay tuned. —Richard I. Gibson  Links:Interview with Jay Shah The South Atlantic Anomaly A really good look at the nature and implications of reversals

It isn’t true that all geologists drink beer. But many do,

and I’m one of them. Today I’m going to talk about the

intimate connection between geology and beer.

Beer is mostly water, and water chemistry has everything to

do with beer styles. And water chemistry itself depends mostly on the kinds of

rocks through which the water flows. You know about hard and soft water – hard

water has more dissolved chemicals like calcium and magnesium in it, and while

salts of those chemicals can precipitate out of hard water, making a scum on

your dishes, they also can be beneficial to development of bones and teeth. In

the United States, the Midwest and Great Plains have some of the hardest water

because of the abundant limestones there, and in Great Britain, southern and

eastern England have harder water than Scotland for similar reasons.

But it wasn’t limestone that made Burton-upon-Trent a center

of brewing in the 19th Century, when it was home to more than 30

breweries. The water there is rich in sulfate which comes from gypsum, calcium

sulfate, in the sandstone underlying the region. Those sandstones are Permian

and Triassic in age, representing a time when much of the earth was arid. Those

dry conditions allowed gypsum to crystallize in the sediments. Gypsum is much

more soluble than limestone, and the slightly acidic waters of Burton help with

that. Burton water has ten times the calcium, three times the bicarbonate, and

14 times the sulfate of Coors’ “Rocky Mountain Spring water” in Colorado. That certainly

makes Coors’ Burton brewery product rather different from that made in

Colorado.

In fact, the addition of gypsum to beer is called

“Burtonization.” This increases the hops flavor, but more important to history,

sulfates act as preservatives in beer, enough so that Burton brews of pale ales

could survive the long trip to British India, giving us the India Pale Ale

style of beer. Not from India, but brewed with sulfates derived from gypsum in

Britain’s rocks.

That slight acidity in Burton’s water depends on the calcium

and magnesium content, and also lends itself to extracting sugars from malted barley

in the mashing process. Calcium and magnesium also help yeast to work its

magic. Today, home brewers can buy “Burton Water Salts” to imitate the product

from England.

Truman, Hanbury, Buxton & Co., Black Eagle brewery, Derby Street, Burton-upon-Trent, in 1876,

from University of London

Less hoppy beers often originated in areas where the sulfate

content of the water was low. Pilsen in the Czech Republic, home to pilsner

beer, has almost no sulfate and only 7 parts per million calcium in its water,

compared to around 300 for Burton. Pilsen is in an area of metamorphic rocks

that don’t yield the typical hard-water-making elements.

The presence of Carboniferous age limestones in Ireland make

waters that are high in calcium and carbonate, but they lack the sulfate of

northern England. Together with other differences, that makes the area around

Dublin ideal for making a stout porter known today as Guinness.

After water, it’s the soil that makes the most difference to

beer. Hops can grow in a wide range of soils, even the decomposed granite we

have here in Butte, but the thick, well-drained soils of Washington and Oregon,

weathered from volcanic rocks, make those states the source of 70% of the hops

grown in the United States.

The surge of craft breweries in the United States has given

rise to some interesting geological names for brews. Great Basin Brewing in

Reno and Sparks, Nevada, has Ichthyosaur IPA, known as Icky, as well as

Orogenesis, a Belgian-style amber ale. Socorro Springs, in New Mexico, brews

Isopod Pale Ale and Obsidian Stout is available from Deschutes in Oregon.  You can get Triceratops Double IPA at Ninkasi

Brewing in Eugene, Oregon, and Pangaea Ale at Dogfish Head in Delaware. And

even though it’s more chemical than geological, we shouldn’t leave out Atomic

Ale’s Dysprosium Dunkelweizen, made in Richland, Washington. Dysprosium is a

rare-earth element found in the phosphate mineral xenotime and other stranger

minerals.

San Andreas Brewing Company, near the fault in California, boasts

Oktoberquake and Aftershock Wheat.

And I’m undoubtedly prejudiced, because I’m the House

Geologist at Quarry Brewing here in Butte, which probably has the best mineral

collection in a brewery in the United States, but I think their collection of

geological names for their beers is unexcelled: Shale Pale Ale, Galena Gold,

Open Cab Copper, and Gneiss IPA, and seasonals including Albite, Basalt,

Bauxite, Calcite, Epidote, Halite, Ironstone, Porphyry, Opal Oktoberfest,

Schist Sour, Rhyolite Rye Pale Ale, Pyrite Pilsner, and more. Mia the bartender

and I tried to come up with a fitting name for a 50-50 mix of basalt and

gneiss. I wanted it to be charnockite, but we ended up calling it Mia’s

Mixture.

Next time you enjoy a beer, thank geology!

—Richard I. Gibson

Image: Truman, Hanbury, Buxton & Co., Black Eagle brewery,

Derby Street, Burton-upon-Trent, in 1876 from University of London

Ganoid fish from an old textbook (public domain)

This is an assembly of the 15 episodes in the original

series from 2014 that are about Paleozoic vertebrates.

I’ve left the references to specific dates in the podcast so

that you can, if you want, go to the specific blog post that has links and

illustrations for that episode. They are all indexed on the right-hand side of

the blog.

Thanks for your interest and support! 

What is dynamic topography? Well, it depends on who you ask. Dynamic topography is similar to other terms, like uplift, that have been used in so many different ways that you really have to look at the document you’re reading to understand what the author is talking about. This term has been applied to places around the world, like the Colorado Plateau in the United States, South Africa, the Aegean, and East Asia, which makes it even more complicated to tease out its meaning. Most broadly, dynamic topography refers to a change in the elevation of the surface of the earth in response to something going on in the mantle. This “something” can include both the flow of the mantle, as well as differences in mantle temperature or density. For the purposes of this podcast, I will use a more strict definition: Dynamic topography is the change in the elevation of the surface of the earth in response to the upward or downward flow of the mantle. How much higher or lower can dynamic topography make the earth’s surface? Well, that’s a matter of debate. Earlier studies have suggested that several kilometers, or over 6000 feet of modern elevations can be explained by things going on in the mantle. More recent work instead suggests that dynamic topography creates changes of at most a three hundred meters, or a thousand feet. A good example of a place where this process is thought to be active is Yellowstone. As Dick Gibson discussed in the December 19th, 2014 episode, Yellowstone is thought to be a hot spot. That is, an area of the earth where hot material moves from deep within the mantle to the base of the crust, causing significant volcanism at the surface of the earth. Other well-known hot spots are located in Hawaii, and Iceland. So how can a hot spot like Yellowstone cause dynamic topography? Well, you’ve probably seen a similar process at play the last time you played in a pool or a lake. Think of the surface of the pool like the surface of the earth. If you start moving your hands up and down under water, the surface of the pool starts to move up and down. If you ever tried to shoot a water gun upwards underwater when you were a kid, you probably remember it pushing up the surface of the water, and being disappointed that it didn’t shoot out at your friend or sibling. As an adult, you could try holding a hose upwards in a pool. Again, it probably won’t shoot out, but will gently push upwards on the surface of the pool. Dynamic topography concept. © Commonwealth of Australia (Geoscience Australia)  2017, used under Creative Commons Attribution 4.0 International Licence The principle for a hot spot creating dynamic topography is the same. The flow of the mantle pushes upwards, warping the crust and increasing the elevation of the earth’s surface above the hot spot. Near Yellowstone, this results in an area of high elevation which lies next to the Snake River plain. But Dynamic Topography doesn’t just cause increases in elevation, it can also pull the earth’s surface downward. In North America, dynamic topography is thought to have been in part responsible for the creation of the Cretaceous interior seaway.  As a reminder, the Cretaceous interior seaway was a shallow sea that covered parts of western North America, in middle to late Cretaceous time, about 100 to 79 million years ago. Its size varied, but at its greatest extent the seaway stretched through Texas and Wyoming in the US, and Alberta and to the Northwest Territories in Canada. It was widest near the US-Canadian border, where it stretched from Montana to western Minnesota. Low elevations in western North America that allowed the ocean to flood in and form this shallow sea may have been caused by downwards flow in the mantle. This downwards flow was likely caused by oceanic crust that was subducted at the western margin of North America. That is, oceanic crust that went underneath the North American plate and into the mantle. Because this crust was par

Today’s topic is three minerals with the same chemical formula: Kyanite, Andalusite, and Sillimanite.  How can three things with the exact same chemical formula, Al2SiO5, be different minerals? Many of you probably recall that besides a distinct chemical composition, a mineral has a definite crystalline structure. And these three minerals each have completely different crystallography. The basic reason for the different crystal structure is that the chemicals aluminum and silicon, arrange themselves differently depending on conditions of pressure and temperature. Kyanite forms at relatively low temperatures over a wide range of pressures while sillimanite crystallizes at relatively high temperatures, generally above 700º C over a similar range of pressures to kyanite. Andalusite develops in a more limited temperature-pressure field, call it medium temperatures but always relatively low pressures. All that variety happens under metamorphic conditions, when rocks are undergoing lots of changes such as those that happen when continents collide, or when subduction scrunches some parts of the crust against others. So that means these minerals are usually found in metamorphic rocks, and in fact they are called index minerals for the particular conditions that they represent. Kyanite is probably the most familiar of the three. It’s often a beautiful blue color, making long, lath-like crystals, so it’s popular with collectors. Kyanite also has a nearly unique, and diagnostic property. Whereas most minerals have a particular hardness, kyanite has two. On the Mohs hardness scale, kyanite is 5 in the direction along the length of the crystals, but 7 across them. Together with the color and crystal habit, this makes kyanite pretty easy to identify. Andalusite and sillimanite are less common. But andalusite also makes interesting crystals, especially when carbon gets included in the growing crystals. That can produce a distinctive elongate four-armed cross, a variety called chiastolite that is sometimes polished to make jewelry. Sillimanite certainly can also make nice crystals, but I guess I’ve led a sheltered life, or maybe I just haven’t mapped enough metamorphic rocks. I’ve never seen a large sillimanite crystal in the wild, just fibrous, wispy, almost feathery coatings in metamorphic rocks like schist and gneiss. So these things are cool collectible minerals and they help geologists figure out the pressures and temperatures that formed rocks, helping unravel the geologic history of the places where they are found. But they also have economic value. Kyanite and andalusite especially are mined to make mullite, another aluminum silicate that’s pretty rare in the natural world but pretty common as a synthetic material made from kyanite. Toilet bowls, which you might call porcelain, are more or less mullite. Most of it is made from a clay mineral, but kyanite can be added to improve its toughness and stability. And small amounts of kyanite go to making abrasives in things like automobile brake shoes. But by far the greatest use of kyanite and andalusite is in making mullite for refractories – ceramics that retain their strength and remain chemically inert at very high temperatures. Furnaces, kilns, and crucibles in the iron and steel industries are often constructed with mullite bricks, and steel making consumes something like 70% of all the aluminum silicates produced worldwide. The United States is the world leader in producing kyanite. It’s mined at four places in Alabama and Georgia, where the metamorphic rocks of the Appalachian Mountains contain abundant reserves. US mine production of kyanite, at about 100,000 metric tons a year, is more than we need, so we export about a third of what we produce – one of only a handful of mineral commodities that the US is self-sufficient in. The total value is around $30 million a year. South Africa produces more andalusite than the US produces kyanite, so it’s the world leader in producing

For today’s episode of the podcast I’m introducing you to Dr. Petr Yakovlev, a friend and geologist here in Butte at the Montana Bureau of Mines and Geology. Petr will be doing occasional guest episodes to give you all a break from my voice, as well as information about some of the diverse things he's worked on. Petr Yakovlev with a Cenozoic conglomerate near Cardwell, Montana. Photo by Dick GibsonPetr got his undergrad geologic education at Boston College and his PhD at the University of Michigan. In this episode Petr and I talk about his work in Tibet, which has implications for the fundamental nature of the India-Eurasia collision; another structural geology project he worked on in the Catskills of New York; and the projects he’s working on here in Montana. And he gives us some teasers about the kinds of topics he plans to cover for History of the Earth. Running time 13 minutes. . 

Today’s Episode takes us to Australia, the home of the Riversleigh Lagerstätte. Lagerstätten, you may recall, are fossil assemblages that typically have extraordinary diversity as well as extraordinary preservation. The Riversleigh Lagerstätte fits that definition well, containing fossils of 15- to 25-million-year-old mammals, including an extinct giant platypus, as well as birds, reptiles, frogs, and lungfish. But the story begins about 500 million years ago, not 25 million years ago. In Early to Middle Cambrian time, more than half a billion years ago, the supercontinent of Gondwana was pretty much assembled, with South America, Africa, India, Antarctica, and Australia comprising a wide, long continent that stretched from the South Pole to north of the Equator. The prong of the continent including Australia was the part that was in the tropics, and much of what is now northern Australia was covered by a warm, shallow sea. In what is now northwestern Queensland, where the Riversleigh Lagerstätte is found, the shallow sea transgressed and regressed – meaning it came and went – and among other things, sediments included grainy shallow-water limestones. The resulting Thorntonia Limestone contains fossils that I’m sure are interesting and informative, including trilobites, brachiopods, and stromatolites, pretty typical of Cambrian rocks. But that’s not the lagerstätte. Nimbadon, a koala-like tree-dweller. From Wikipedia.Fast forward about 475 million years, to the Oligocene epoch of the Paleogene Period of the Cenozoic Era. The rocks of northern Queensland were dissolving in a warm, wet, tropical environment, and the limestones of the Thorntonia formation were developing karst topography – caves and surficial pools rich in dissolved calcium carbonate. Starting about 25 million years ago, near the end of the Oligocene, animals began to die in those pools and become trapped in the caves, where ongoing calcium carbonate deposition preserved them remarkably well. So even though the origin of the calcium carbonate was a really ancient rock, the Cambrian Thorntonia formation, it was the much more recent dissolution of those rocks that provided the material that preserved the fossils at Riversleigh. Ages of the fossils extend from late Oligocene time into Miocene, around 15 million years ago, but there are younger fossils as well since the caves are still there and deposition is continuing.   The Riversleigh site is not just one location, but many, spread out over a hundred-square-kilometer area that was named a World Heritage Site in 1994. Riversleigh contains the richest assemblage of bat fossils in the world – at least 35 different species. Besides bats, mammal fossils include extinct koalas, marsupial lions, wombats, herbivores the size of sheep, at least 14 species of opossum, and 15 different kangaroo species. While many fossils are remarkably well preserved, some, such as Yalkaparidon, are only known from a few teeth and scattered bones, making their relationships to other families uncertain. In fact, some are grouped colloquially as Thingodonta, meaning “toothed thing”. Some researchers have suggested Yalkaparidon was a mammalian woodpecker. Bird fossils at Riversleigh range from extinct flightless rails to storks and lyrebirds. Reptiles are represented by tree-dwelling crocodiles, horned turtles, and dragon lizards, which were probably related to iguanas. There are even snakes and frogs and two species of lungfish, all of which are really rare in the fossil record, especially as long ago as the Riversleigh assemblage, 15 to 25 million years. Some lagerstätten record essentially an instant in geologic time, or a relatively short period. An example of such an assemblage is the fish of the Green River Formation in Wyoming, many of which may have been killed in a single event – a heavy fall of ash into the lake where they lived, from an erupting volcano. So Riversleigh, in addition to its diversity and excellent preservation

Today for episode 381, we’re going to Zealandia. No, it’s not a quirky TV show modeled after Portlandia. It’s the 7th largest continent on earth. We’re not talking continents in the geographic sense, really large land masses like Africa and South America, but we are talking about continental material in the geologic sense, even though most of it is submerged beneath the ocean. Public Domain via WikipediaZealandia is centered on New Zealand, and in some ways, it’s been known for decades, ever since good charts of subsurface bathymetry were created. Those data show a complicated mix of rises and troughs on the sea floor around New Zealand, including the Lord Howe Rise in the Tasman Sea between New Zealand and Australia, the Campbell Plateau east of New Zealand, and other highs and lows. Although the ocean floor around the globe is diverse, with seamounts and trenches, fault zones and piles of volcanic rocks here and there, on the whole oceanic crust is deep and uniform, or at least varying broadly and predictably. These relatively small-scale high plateaus on the ocean floor around New Zealand are unusual. Let’s define a continent. Geographically, it usually means a large land mass. “Large” is subjective, but Australia, at about 9 million square kilometers, is considered to be the smallest continent. And the count depends on whether you separate Europe from Asia, or just say Eurasia as one, and other conventions. Many would say that a degree of isolation and separation also defines a continent, so Eurasia should be one, together with Africa, North America, South America, Antarctica, and Australia, for a total of six. Forget all that. We’re looking at places made of continental crust, the generally lighter, silica-rich material in contrast to oceanic crust, denser and more iron-rich. By that geologic definition, all the conventional continents really are mostly continental crust too. All well and good. There are numerous smaller, separated areas of continental crust that are usually called microcontinents. Madagascar is probably the best example of a microcontinent, but there are lots of them, and you can get into plenty of arguments about whether a piece like, say, Greenland, is or is not fully a part of the North American continent. So, let’s go to Zealandia. In 2017, Nick Mortimer and colleagues, writing in GSA Today, pretty much laid any argument to rest. There’s abundant evidence to say that there is a large, diverse terrain centered on New Zealand but 94% submerged, that is mostly continental crust. It adds up to about 5 million square kilometers, comparable in size to Arabia and India, sub-continents that are connected in one way or another with full-fledged continents. Zealandia is close to, but clearly separated from Australia, and Mortimer and others make a convincing case that it should be considered the seventh continent, six times larger than Madagascar, the biggest microcontinent. So if continental rocks are lighter, which accounts for them being for the most part above sea level, why is most of Zealandia under water? The crust there is thinner, so it doesn’t rise as high as that on most continents, and it has been stretched and broken, partly rifted apart during a long complex history. Zealandia was probably originally part of the supercontinent of Gondwana, attached to eastern Australia and West Antarctica, when those two continents were fully attached to each other about 105 million years ago, in Early Cretaceous time. That margin of Gondwana, thousands of kilometers long, was a subduction zone somewhat like today’s Andes, with an old Pacific oceanic plate diving beneath the Gondwana continental crust. There would have been a volcanic mountain range there, recorded in Zealandia as a surviving string of granitic rocks, batholiths similar to those that developed in western North and South America during Mesozoic and Cenozoic time and continuing to this day. Gondwana began to be rifted apart by about 85 million yea