Geology in Pop Culture - The Rescuers Down Under

 Geology in Pop Culture

Released in 1990, The Rescuers Down Under continues the escapades started in 1977's The Rescuers. However, in this adventure our favorite mice, Bernard and Bianca, travel down to the Australian outback (not the steakhouse). Here, they find that the villain of the story, the poacher Percival C. McLeach has kidnapped a boy, Cody, while hiding out in some abandoned opal mines.

 

So what exactly is opal anyway?

Different types of Australian opal varieties. Image courtesy of BlackOpal Direct. 

Opal (SiO2.H2O) is a mineral that forms from the packed spheres of silica (SiO2), also known as the mineral quartz. Opal is a hydrated form of silica where water has been shown to include between 3 and 9% of the total mineral structure. Unlike many minerals, because of how it is formed, opal is amorphous, or without form. This means that there is no crystal structure or cleavage that is seen in most other minerals. Opal forms through the processes of solidification of gelatinous or liquid silica within cracks and voids of other rocks. 

Since the opals are created by spheres of silica and water, the size of the sphere's dictates the colors that are produced. These colors are refracted through the opal like a prism, with larger spheres yielding red or orange, and smaller ones radiating blue. However, this is only the case with precious opals, the more gem quality ones. Most opals, ~95%, are referred to as common opals. These are opals that do not have the "play-of-color" expected in opals as seen in the image above. Although still beautiful, they are harder to identify than the precious opals. 

Location of Australian Opal Mines. Image courtesy of Opals Down Under. 

Despite being found around the world, it turns out that ~95% of the world's supply of precious opals comes from Australia. The opals started to form during the Cretaceous period when there was a large inland sea across Australia. During this time silica rich sands were deposited along the shorelines, then 30 million years ago, during the Tertiary, deep weathering of these sediments within the Australian Artesian Basin released large amounts of soluble silica into the groundwater. This silica traveled into the cracks and fissures in the Cretaceous age rocks where it was stopped by an impermeable layer below. Staying in the cracks and fissures, the opal deposits formed veins, often trapping fossils that also happen to be in the sedimentary rocks such as leaves, dinosaurs, small mammals, and marine reptiles such as Eric the Pliosaur. 

Eric the opalized pliosaur. Image courtesy of Opal Auctions. 

Most of the opal mines in Australia are a type known as open-cut. This means that they basically dig down to the source of the deposit, in this case opal, and clear out anything above it, forming a quarry or pit. This limits the dangers of enclosed mine spaces, allows you to find smaller deposits easier, is much faster with heavy machinery, but is also much, MUCH, more damaging to the environment, destroying literally everything to get to the deposits. 

In The Rescuers Down Under though, they are clearly not in an open-cut mine, they are underground mines. There are some underground opal mines that are found within Australia. One of these locations is the town of Mintabie, found near the north-central portion of the South Australian state. And although they did use open-pit mining in Mintabie, they also had quite a number of underground mines as seen in the picture below.

Mintabie Opal Mines. Image courtesy of Opal Auctions. 

What makes Mintabie interesting is that the mining heyday here was in the 1980's. Even though opals had been know from here since the 1920's, production increased starting in 1976 with the addition of mining equipment able to break through the hard sandstone. During the 1980's, production here was the largest in all of Australia with a peak during 1988. However, after 1988, production quickly declined resulting in lots of abandoned opal mines. 

Warning sign in The Rescuers Down Under

This timing of the opal mines being abandoned during the late 1980's correlates strongly with The Rescuers Down Under, which would have been starting to be in production probably ~1988. Seeing these abandoned opal mines pop up all over the place would have been a good impetus to a setting for their movie. 

References
https://blackopaldirect.com/opal-types/

https://www.opal.academy/opal-basics

https://www.opalsdownunder.com.au/learn/what-is-opal/

https://jasonree.com.au/blogs/news/why-are-australian-opals-so-expensive

https://www.opalsdownunder.com.au/learn/australian-opal-mining-fields/

https://www.opalsdownunder.com.au/learn/how-is-opal-formed/

https://www.ga.gov.au/education/minerals-energy/australian-mineral-facts/opal

https://www.nationalopal.com/opals/precious-opal-formation.html

https://www.opalauctions.com/learn/opal-information/eric-the-opalized-pliosaur

https://www.opalauctions.com/learn/news/mintabie-town-to-close

https://www.uniqueopals.ch/opal-origin.htm

Geology Through the Radio - Honky Cat

 

While many songs have the possibility to be examined in a geological sense, there are few as blatant with their geological references as Elton John's "Honky Cat"

Honky Cat

When I look back, boy, I must have been green

Bopping in the country, fishing in a stream

Looking for an answer, trying to find a sign

Until I saw your city lights, honey, I was blind

They said, get back, honky cat

Better get back to the woods

Well, I quit those days and my redneck ways

And, mmhm-hm-hm, oh, change is gonna do me good

You better get back, honky cat

Living in the city ain't where it's at

It's like trying to find gold in a silver mine

It's like trying to drink whiskey, oh, from a bottle of wine

Well, I read some books, and I read some magazines

About those high-class ladies down in New Orleans

And all the folks back home, well, said I was a fool

They said, oh, believe in the Lord is the golden rule

They said, get back, honky cat

Better get back to the woods

But I quit those days and my redneck ways

And, ooh, ooh, ooh, ooh, oh, change is gonna do me good

They said, get back, honky cat

Better get back to the woods

Well, I quit those days and my redneck ways

And, oh, oh, oh, oh, oh, change is gonna do me good

They said, stay at home, boy, you gotta tend the farm

Living in the city, boy, is, is going to break your heart

But how can you stay when your heart says no?

How can you stop when your feet say go?

You better get back, honky cat

Better get back to the woods

Well, I quit those days and my redneck ways

And, ooh, ooh, ooh, ooh, oh, the change is gonna do me good

You better get back, honky cat

Living in the city ain't where it's at

It's like trying to find gold in a silver mine

It's like trying to drink whiskey, oh, from a bottle of wine

Oh, yeah

Get back, honky cat

Get back, honky cat

Get back, woo

Get back, honky cat

Get back, honky cat

Get back, woo

Oh, get back, honky cat

Get back, get back, honky cat, woo

(Oh yeah, redneck ways and, woo)

Geology

While not pervasively throughout the song, there is one line that pops up a couple of times: "It's like trying to find gold in a silver mine". While this might seem like a simple phrase because who would go looking for gold in a silver mine, the formation of gold and silver deposits are linked and they are actually found together quite frequently. In many silver mines, gold typically accounts for 0.5-5% of production because gold and silver veins (along with many other precious metals) are produced from the cycling of hydrothermal waters surrounding a volcano.

Mineral vein creation from hydrothermal fluids. Image courtesy of web-japan.org. 

Magma's have all sorts of dissolved elements and minerals in them. As the magmas heat up the surrounding countryside near a volcanic source (or potential volcano) also heats up. This includes the groundwater, producing hydrothermal fluids that becomes enriched in the minerals from the magma as well as minerals from the surrounding rock. As these fluid travel through cracks and fissures of the much cooler rocks further away from the magma, the fluids cool down and mineral deposits are precipitated. 

View of the Bingham Canyon Mine facing west

The presence of these precious metals also indicates something else about the environment. Even if there is no volcanic activity at the moment in these areas, it means that there was once volcanic activity there. Utah's Bingham Copper Mine is a perfect example, where there is clearly no volcanic activity anywhere currently near the mine, however, at one point in the past there must have been, because of the deposition of not only a large abundance of copper, but also silver and gold within the mine. 

Diagram of the Farallon Plate subduction zone along the western United States. Image courtesy of the NPS.

I go into more detail on the Bingham Copper mine HERE, however a short version of it is that at one time there was a subduction zone along the western coast of North America that produced volcanoes across the western US. Around 30 to 40 million years ago, that line of volcanoes was located within Utah. Magma was slowly injected into the Oquirrh Mountains, predominantly into the 300 to 350 million years old rock formation known as the Oquirrh Group. These rocks, laid down in the Carboniferous (i.e. the Pennsylvanian and the Mississippian), are composed mostly of quartzites and limestone beds. This magma body slowly cooled to form what is known as the Bingham Stock, an igneous body identified as a monzonite porphyry. In addition to the magma body itself, is that the hot magma produces a lot of hydrothermal fluids within proximity of the magma body. These hydrothermal fluids move the heavy metals (such as gold, copper, silver, etc.) from within the magma and redeposit them within the surrounding landscape. 

So the Utah version of this is "It's like trying to find gold in a copper mine"

You can see the rest of the Geology Through the Radio postings on my website.

Geology Through Literature - The Periodic Table

Geology Through Literature: The Periodic Table

The Periodic Table was a rich experience with the author, Primo Levi, recounting several stories within his life through the framework of elements on the Periodic Table, hence the name of the book. But here we are interested in the "geology" through literature, not chemistry, so what does this book have to offer us? Quite a bit actually. Here are some of the more geological sections.

First Chapter - Argon

"...[this] Piedmontese dialect, never written except on a bet, and the Hebrew inlay, snatched from the language of the fathers, sacred and solemn, geologic, polished smooth by the millennia like a bed of a glacier."

Although there are known instances where glaciers have moved quickly, they are generally known to have a slow pace to them. Hence the term "glacial" meaning slow. But over time, as the glacier moves, the base of the glacier defrosts and refreezes continually. This defrosting and freezing causes the base of the glacier to pick up various pieces of rocks, gravels, sand, and rock powder. These pieces of the landscape are then forced downwards by the weight of the overlying ice, which can sometimes reach many miles in thickness. These rock pieces, that are being forced downwards as the glacier moves forward, have the effect of acting like sandpaper on the surface of the Earth, slowly polishing the bedrock smooth. Over time that smoothness is ground down finer and finer. This polishing effect also produces powered rock known as glacial flour, just like sandpaper does to a piece of wood.

Sixth Chapter - Nickel

"Yes, all mines are magical per se, and always have been. The entrails of the earth swarm with gnomes, kobolds (cobalt!), nickel, German 'little demon' or 'sprite,' and from which we derive the word nickel, creatures who can be generous and let you find a treasure beneath the tip of your pickax, or deceive and bedazzle you, making modest pyrites glitter like gold, or disguising zinc in the garb of tin: and in fact, many are the minerals whose names have roots that signify 'deception, fraud, bedazzlement.'"

This passage is interesting because it touches on a couple of different aspects of minerals. One is their sometimes resemblance to other, more or less important minerals. And the other is the naming of the minerals, which sometimes goes so far back in history that their original names don't have any direct correlation with what they are known for today.

Visual comparison of Pyrite to Gold from GeorgiaGold.Com

One of the most commonly misidentified minerals would probably be pyrite for gold. Pyrite, often known as "fool's gold", has a strong gold colored metallic luster to it, where people are immediately drawn to assume it is gold.  Pyrite is actually a fairly common mineral, especially when compared to the far more valuable and elusive gold. Pyrite is made up of iron and sulfide (FeS2), while gold is just made up of elemental gold (Au). The name "Pyrite" comes from the Greek word "Pyr", which means "fire". The name comes from the fact that when it was struck with an iron tool back in ancient times it emitted sparks.

The mineral cobalt. From Mining.com.

The name of the mineral cobalt originally came from the German word for goblin or devilish spirit, kobold.  Around 1500 AD (BCE), German miners were mining for silver when they came across this substance, which looked like silver but did not act like silver. And to top it off, when they tried to melt it down it gave off noxious fumes, which caused the miners to get sick and sometimes die. They attributed it to goblins having bewitched the silver ore causing the noxious fumes. One of the problems was that the primary metals known at the time: gold, silver, copper, iron, tin, lead, and mercury,  were the only known metals since ancient times and the miners had no concept that new metals could even exist. In the 1730's a Swedish chemist, Georg Brandt, was able to isolate the metal and ended up using the same name that the German miners had branded it with.

A small chunk of nickel from Live Science. 

In the 1600's the Germans were at it again. This time miners were searching for copper and came across this brownish-red rock that they believed was copper. However, when they tried to extract the copper from the rock they were unsuccessful. They ended up blaming "Nickel" for the lack of copper, who was a mischievous German demon. They called the ore kupfernickel, which means "copper demon". In 1751, another Swedish scientist, Baron Axel Fredrik Cronstedt, was able to extract the nickel from the kupfernickel ore, which was a mixture of arsenic and nickel. He ended up dropping the first part of the name and kept the "nickel" part as the name of the element and mineral. 

Eighth Chapter - Mercury

"That very evening just before nightfall, we heard a great rumble of thunder, as though the island itself was being shaken to its roots. In a few minutes the sky darkened and the black cloud that covered it was lit from below as by a fire. From the top of Mount Snowdon we saw first rapid red flashes leap out and climb up into the sky, then a broad, slow stream of burning lava: it did not descend toward us but to the left, the south, pouring from ridge to ridge, hissing and crackling. After an hour it reached the sea and there it was doused with a roar, lifting up a column of vapor. None of us had ever thought that Mount Snowdon could be a volcano; and yet the shape of its summit, with a round hollow at least two hundred feet deep, could have made us us suspect this. 

The spectacle continued all through the night, calming down every so often, then picking up again with a new series of explosions; it seemed that it would never end. Yet, toward dawn, a hot wind blew from the east, the sky cleared off again, and the uproar gradually died down until it was reduced to a murmur, then silence. The mantle of lava, which had been yellow and dazzling, turned reddish like smoldering coals, and by daylight it was extinguished."

Map of Desolation Island highlighting Mount Snowdon from The Periodic Table

Unfortunately,  Desolation Island, and the mysterious volcano Mount Snowdon, were both made up for the story. I had hopes that they would really exist given the autobiographical nature of the rest of the story, however this chapter was one based entirely in fiction. The original Mount Snowdon, the one from which the story's volcano was named, was formed during the Ordovician period (450 million years ago) along a prehistoric convergent plate boundary in what is now Whales. A convergent plate boundary is when one plate was forced down underneath another plate. This caused the lower plate (the one going down into the Earth) to melt. The liquid rock, magma, then slowly rose over time and ended up forming volcanoes, like the aforementioned Mount Snowdon (the real one). The real Mount Snowdon however has long been an extinct volcano and has been eroding ever since.

Simplified map of the Mediterranean plates showing the subduction zones. From Ring et al, 2013. 

Although it is never spelled out, there are a couple of locations for which the island could be located. One of those is the Mediterranean based on the eruption style. Within the Mediterranean you have an over abundance of islands, many of which are either volcanoes or volcanic in origin. This is because you have the same situation as the formation of Mount Snowdon (the real one). There are numerous subduction zones, creating numerous volcanoes across the region, specifically in Italy and Greece. These volcanoes form as the subducted plate starts to melt and that melted plate material, the magma, rises up through the crust. Eventually, as more and more magma builds up, the pressure builds up and the volcano erupts. When the magma moves through continental crust it picks up more silica based minerals, which melt at a lower temperature and produce more explosive eruptions, like the ones seen from Mount Vesuvius. The story of Mount Vesuvius/Pompeii is very reminiscent of the story that Levi told in the The Periodic Table with lava and ash clouds erupting from an unknown volcano.

However, Levi points out at the beginning of the chapter that Desolation Island is located 1,200 miles to the southeast from an island known as St. Helena. St. Helena is actually a real volcanic island that is located in the middle of the southern Atlantic Ocean. It's claim to fame is that it was the location of Napoleon's final exile/imprisonment and where he eventually died. Although the island is a volcano, it's last eruption was 7 million years ago, when the island was situated along the Mid-Atlantic Ridge. The Mid-Atlantic Ridge is a divergent plate boundary, which means that two plates are pulling apart from each other. This pull-apart results in a very long volcanic mountain chain located beneath the oceanic surface. While most of the volcanoes remain below the surface of the ocean, some do break the surface, with St. Helena being one of those examples. Eventually the island moved along with the plate as the plate spread out from the divergent plate boundary. This movement moved the volcano away from its source of magma, making it an extinct volcano, likely never to erupt again. The type of eruption that came from St. Helena would be vastly different than the one from Pompeii as well. While Pompeii would contain an explosive eruption with lots of ash and volcanic gasses and clouds, St. Helena would more resemble a Hawaiian eruption, with a steady stream of low-viscosity lava and very little clouds.

 References
https://www.georgiagold.org/2018/08/05/pyrite-vs-gold-how-to-spot-the-difference/
https://www.forbes.com/sites/davidbressan/2016/07/18/the-origin-of-geological-terms-pyrite/#fa2cc446e96e
https://www.sciencefriday.com/articles/the-origin-of-the-word-cobalt/
https://www.livescience.com/29327-nickel.html
https://www.walesonline.co.uk/news/local-news/seen-last-snowdons-volcanic-past-1826956
https://volcanocafe.wordpress.com/2013/01/01/mt-snowdon/
Ring, U., Gessner, K., Thomson, S., & Markwitz, V. (2013). Along-strike variations in the Hellenide Anatolide orogen: A tale of different lithospheres and consequences. Bulletin of the Geological Society of Greece, 47(2), 625-636.
http://sainthelenaisland.info/geology.htm

Geology Fun Fact - Most Common Mineral

Geology Fun Fact

Question: What is the Earth’s most common mineral? 

Looking at the bulk composition of the Earth, the most common mineral is a silicate mineral with a perovskite structure that dominates the lower mantle. This mineral has recently been named “bridgmanite”.

Here is a story about the naming of this mineral.

Click HERE for more Geology Fun Facts!

Geology Fun Fact - Common Minerals

Geology Fun Fact

Question - What is the most common mineral in the crust and surface of the Earth? 

Answer: Depending on how you look at it there are two possible minerals. Quartz is the most common mineral on the surface of the Earth, but Feldspar is the most common mineral in the crust. Feldspar though, is commonly considered a group of minerals, which includes Potassium-Feldspar and Plagioclase.

Click HERE for more Geology Fun Facts!

Geology Fun Fact - Ice

Geology Fun Fact

Theory: Ice is a Mineral. 

Minerals are defined by being an inorganic, naturally forming, substance with a definite chemical composition, and usually a definite crystal structure.  All of which ice satisfies. So, by definition, ice is a mineral. Just one with a significantly lower melting point than most people are usually accustomed to.

Click HERE for more Geology Fun Facts!

Geology Fun Fact - Birthstones

Geology Fun Fact

Theory: Birthstones are minerals or gems. 

Actuality: Only 11 of the 12 birthstones are minerals. Minerals are naturally occurring substances with definite properties. The 12^th, pearls, are not naturally occurring, they are produced biologically by mollusks.

Click HERE for more Geology Fun Facts!

Geology Through Literature - Idylls of the King

The next up on my Geology Through Literature thread is Idylls of the King by Alfred Lord Tennyson published between 1859 and 1885. You can get my complete thoughts on the book/story over at my blog - The Remnant, but for here I will just go into the geological or basic scientific aspects that are brought up in the story.

The story is an epic poem based on the life of King Arthur. There is only one geological instance worth noting in the story itself.

"Chapter": Gareth and Lynette

"In dewy grasses glistened; and the hair 

All over glanced with dewdrop of with gem 

Like sparkles in the stone Avanturine."

Avanturine, more commonly spelled Aventurine, is a gemstone variety of quartz (SiO2). However, unlike the typical varieties of quartz like amethyst, smokey quartz, or milky quartz (to name a few), aventurine contains flecks of mica and other materials incorporated into the crystal. It is these flecks that give the crystal a "sparkle" as the poem states (geology.com).

A green variety of aventurine. 

Aventurine was named after the Italian words "a ventura", meaning by chance. This is in reference to the chance creation of the artificial aventurine variety now referred to as goldstone where flecks of copper were incorporated into a bit of glass creating a similar, but much more dazzling, appearance (mindat.org).

Goldstone, an artificial "gemstone" similar to aventurine in appearance, except it is often made with glass and copper flecks or other metals (wikipedia).

Geology in Pop Culture - Activity Rocks Kit

Recently while at Death Valley National Park, my wife purchased a geology activity for me to do with our daughter. And since this is a fairly fun and easy activity to do with kids I figured I would pass along the information. You can get the Activity Rocks kit at Amazon right now as well.

Above you have the four rock/mineral based activities that comes with the kit. The rocks/minerals are:

• Magnetite - and a paperclip for magnetic properties
• Pumice - for a floating rock
• Quartz pebbles - for a sparking rock activity
• Dolomite - With a penny for a dissolving and recrystallization activity.

Many, if not all, of these rocks are available to most geologists, however this kits gives them in nice kid friendly sizes with instructions (below) for what to do with them, 

Here is everything at the start. The pumice is floating, the dolomite is sitting in vinegar, the magnetite is magnetizing, and the quartz pebbles are just sitting there. The best part about this kit is after you are done with it you can pass it on to a friend for them to experiment with as well. 

Besides the pumice and the magnetite, which are neat, but you can't really do anything beyond float or stick something to it, the real science comes with the dolomite and the quartz.

Here is the dolomite after it had been sitting in vinegar for about a week. The crystals recrystallized nicely on top of the rock. There is also a penny in the solution, which was supposed to turn the crystals blue (due to oxidation of the copper). They did turn blue at first, but only slightly and not really noticeable after a while.

Now the really interesting thing (that I had not realized before), was that when two "tumbled" quartz pebbles (crystal quartz in this instance) are struck together they produce an electrical shock that lights up the pebbles. This was a little hard to picture so I had my daughter take some photos while I struck the pebbles together. Below are the sequence of photos and a very brief video that shows the results.

All in all a fun activity to get your kids interested in the joys of geology and science. Also, if buying a kit like this isn't your style, this post will give you info on how to build a kit of your own from your own supplies.

Guest Post - Naturally Harmful Metals and Minerals

Next up in the in the guest blog domain is Eric Stevenson who wanted to write about how natural "stuff" could be potentially hazardous to one's health. Check it out below:

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Naturally Harmful: The Modern and Historical Use of Asbestos, Lead, and Mercury

When a substance is known as “naturally-occurring,” we have a tendency to think of it as something that is possibly beneficial, or at the very least benign – certainly not harmful. However, many metals and minerals that occur naturally in the Earth’s crust are toxic to humans. In some cases, their deadliness was known from the beginning; in others, their usefulness obscured or outweighed the symptoms that warned of their toxicity.

Asbestos
Asbestos was once considered a “miracle mineral.” Ancient Greek writers told stories of tablecloths that could simply be tossed in the fire after use, emerging not only unscathed, but cleaner and whiter than before. Medieval alchemists were so entranced with this material that they hypothesized it came from the hair of salamanders, which could walk through fire and survive. By the time of Marco Polo, however, people knew that asbestos was mined from the earth.

In 1820, an Italian scientist became the first to run a successful business based on asbestos products – fireproof clothing sold all over Europe. Soon after, many items began to incorporate asbestos into their design: stage curtains, gaskets and packing for steam engines, paint and tar paper, and cement. The inclusion of asbestos in construction materials would continue into the 1970s for the simple reason that asbestos was an incredibly effective flame retardant. No doubt countless lives were saved from fire.

However, this “miracle mineral” was not the safety boon it appeared to be. When asbestos-containing products sustain damage, tiny, needle-like fibers are released into the air. Once inhaled, these fibers can cause serious health problems, including lung scarring, asbestosis, and mesothelioma, a rare and deadly form of cancer. One reason this cancer is so dangerous is that mesothelioma symptoms can take anywhere from 20-50 years to surface after exposure, by which time the disease is often in its final stages. Because of these dangers, asbestos has largely been replaced with alternative fire-resistant substances in newly-manufactured construction materials.

Lead
A soft, malleable metal, lead is useful for its low melting point, high density, and resistance to corrosion. It was accessible and easily worked with, and therefore made the ideal medium for the famed plumbing system of the Roman Empire. Lead was not only used for pipes, but also as a component in coins, flatware, cosmetics, spermicide, and food seasonings.

However, even the ancient Romans understood that exposure to lead had serious health-related consequences. As we now know, even low levels of exposure can cause chronic lead poisoning. The dangers of acute lead poisoning were apparent in Renaissance Europe, where it may have been used in some royal assassinations. In modern times, lead was used as a fuel additive, despite early evidence that the vapors were toxic to the workers producing it.

Though lead was removed from gasoline – as well as other products like pipes and house paint – beginning in the mid-1970s, the metal continues to be used in products from car batteries to radiation shielding. Unlike asbestos, lead can still be found in many construction materials because it usually has to be ingested to be poisonous. Initial symptoms of lead poisoning – including headache, abdominal pain, memory loss, and kidney failure – may be confused with other conditions, though more severe neurological problems soon follow. Like asbestos, there is no amount of lead ingestion, however small, that is considered “safe.”

Mercury
Mercury is notable for being one of the few metals that exists as a liquid at room temperature. Historically, mercury had a wide variety of applications, from the practical (preserving wood, developing daguerreotypes) to the recreational (handheld games, fishing lures). Amazingly, both the ancient Chinese and the ancient Greeks thought of mercury as a substance that promoted good health and long life, and doctors continued to use it into the 20th century to treat conditions ranging from depression to constipation to syphilis.

In modern times, most people know mercury as the liquid in thermometers, though it is also found in other measurement devices such as barometers (air pressure) and sphygmomanometers (blood pressure). Thimerosal, an organomercury compound, has been used as a component in dental amalgam and a preservative in vaccines. The latter use triggered a controversy over the possible role of thimerosal in the development of autism, though the most recent studies do not support a link between the two. Regardless, the FDA reports that thimerosal has been phased out of nearly all vaccinations required for young children.

However, parents are right to be concerned about exposing their children to any form of mercury. The substance is extremely dangerous if ingested, inhaled, or absorbed through the skin. Like lead, mercury poisoning affects the central nervous system, resulting in symptoms as diverse as sensory impairment, lack of coordination, hallucinations, and social phobia. Despite the dangers, small amounts of mercury can still be found in certain cosmetics, fluorescent lamps, neon signs, and telescopes.

If you would like more information about any of these substances, please visit:

James E. Alleman and Brooke T. Mossman. “Asbestos Revisited.” Scientific American, 1997.
http://virlab.virginia.edu/Nanoscience_class/lecture_notes/Lecture_14_Materials/Asbestos_CNT/Sci%20Am%20-%20Asbestos%20Revisited%20-%20July%201997.pdf

Jack Lewis. “Lead Poisoning: A Historical Perspective.” EPA Journal, 1985.
http://www.epa.gov/history/topics/perspect/lead.htm

U.S. Food and Drug Administration. “Thimerosal in Vaccines.” FDA.org, 2010.

http://www.fda.gov/BiologicsBloodVaccines/SafetyAvailability/VaccineSafety/UCM096228