12 / OutdoorIllinois July 2011
An ancient, volcano-like
formation known
as Hicks Dome
always has been a
geologic oddity in
Illinois.Now, its rare
earth metals make
this Hardin County
hill a mountain of
potential for today’s
technology.
Story and Photos By
Joe McFarland
Test your Illinois geology
trivia: Did you know an
actual volcano almost
formed once in Illinois?
To be accurate, our state
wasn’t exactly a state when it hap-pened.
In fact, dinosaurs weren’t even
around yet, which was a good thing
for dinosaurs. The fiery, gaseous blast
that created the closest thing to a vol-cano
Illinois has ever known “would
have killed everything around here.”
That’s according to one Illinois
geologist who’s studied the unusual
Hardin County formation known as
Hicks Dome.
It started underground one day mil-lions
of years ago with an explosive
burp in what is now extreme southeast
Illinois. Imagine a volcanic surge of
magma suddenly racing upward and
pushing through the earth’s crust—but
not completely. Torrents of hot gas and
magma blasted toward the surface at
supersonic velocities, shattering
bedrock, mixing and reforming miner-als
and elements along the way in the
searing heat. It’s likely the area would
have been showered with flying
bedrock from the blast.
And then the Earth resumed busi-ness
as usual. Volcanic activity ceased
in Illinois.
In a land that’s known for outcrops
of predominantly 300 million-year-old
sedimentary bedrock, such as lime-stone
and sandstone, the sudden blast
on that day 270 million years ago
pushed up from beneath those layers
truly ancient Devonian bedrock, raising
it some 4,000 feet toward the Earth’s
surface.
It left behind an igneous, mineral-filled
lump on the landscape we know
today as Hicks Dome. It’s a strange mix
of rocks found nowhere else in our
state. Long ago mining operations in
the area tapped into the associated
fluorspar deposits nearby. Our state
mineral—fluorite—formed there, prob-ably
as a result of the igneous blast and
geologic shifts that followed. And while
much of the local fluorspar mining
operations have been idle since the mid
1990s, mining for various grades of
limestone continues at a few Hardin
County quarries.
But could there be something more
precious hidden in the rocks of Hicks
Dome? Geologists have known for
years that trace amounts of unusual
mineral-metals such as yttrium and lan-thanum
occurred in the rocks at Hicks
Dome. Commonly known as rare earth
metals, these obscure metals were of
minor economic importance to the
mining industry for two basic reasons:
For one, they simply didn’t occur any-where
on Earth in large concentrations,
hardly enough to make mining worth-while.
Trace amounts embedded within
rocks made extraction technically diffi-cult.
Second, up until recently, the
world had little use for such metals,
despite the fact many of the metals
exhibited novel “tricks” that they could
perform, such as igniting at room tem-perature.
For example, a rare earth
metal alloy can produce sparks when
scraped (more trivia: ordinary cigarette
lighters use this rare earth metal—not
flint—to produce sparks). Another rare
earth metal has been used to produce
the red color in TV screens.
Aside from these relatively minor
industrial demands, mining and process-ing
of rare earth metals remained a mar-ginal
business as recently as the 1980s.
Then came the technology revolu-tion.
Microchips, ultra-tiny computers
and batteries that seem to last forever
in portable electronics all tapped into
the magic of rare earth. Demand for
these metals turned red hot as engi-neers
and scientists figured out how to
harness those unusual tricks. Need a
superconductor that performs under
high heat? Thank rare earth metal.
Need a Green car with a battery capa-ble
of long highway miles—or a wind
turbine that maximizes electrical out-put?
Thank rare earth metal. Anyone
with a cell phone, an iPod, Blackberry
or practically any other electronic mira-cle
can thank the rare earth metals that
make them all possible.
Now, with today’s global interde-pendence
on new technologies, the
world’s supply of rare earth metals has
the world scrambling. China has long
been in the business of mining and pro-cessing
ores that contain rare earth met-als.
In fact, by some estimates, China
produces nearly 98 percent of the rare
earth metals used today.
But China isn’t the only source of
rare earth. In fact, technically speaking,
rare earth is a misnomer because rare
earth isn’t rare.
“Rare earth metals are found world-wide,”
explained Illinois State Geologi-cal
Survey Geologist Brett Denny. He
said tiny amounts of these metals show
up in everything from granite to ordi-nary
dirt. “Even water in the ocean con-tains
trace amounts. But the reason
why these rare earth metals are consid-ered
rare is because they don’t occur in
significant concentrations.”
Unlike traditional mining operations
that excavate thick beds of pure coal
or limestone, rare earth metals usually
are found embedded as microscopic
Illinois State Geological Survey
Geologist Brett Denny collects a
shale sample at a creek near Hicks
Dome in Hardin County.
The Digital Age and all of its
micro-sized electronic wonders
depend upon unusual elements
commonly called rare earth metals.
Iron oxide stains the uplifted shale
at a Hicks Dome rock outcrop.
The strong odor of natural gas can
be detected in these rocks.
July 2011 OutdoorIllinois / 13
