Stories in Stone (30 page)

Pulling out several wonderful and colorful geology maps, Conti showed us that we were at the base of the Miseglia valley,
one of three quarry valleys around Carrara.
To the north lay Torano and to the south Colon-nata.
Each cut back into the Apuans
for several miles and each had quarries first opened originally by the Romans.
No one knows how many quarries have pierced
these mountains, but one estimate runs as high as 650.
Conti’s geologic maps from 2000 listed 187 quarries.

“We are standing here at the edge of this tectonic window of marble, surrounded by sediments,” said Conti, as he pointed to
an oval of blue and purple on a geologic map of Tuscany that he had spread on his car.
Blue and purple indicated metamorphosed
rocks, mostly marbles but also some schists.
Butter and pumpkin colors showed limestones, sandstones, and shales.
The Apuan
Alps were the largest zone of blue—representing an area about ten miles wide by eighteen miles long—on the entire map.

The Carrara began life as one of those limestones 200 million years ago, about the same time the brownstones began to form.
North America and Africa had begun to split apart from each other, opening the chasm that would grow into the Atlantic Ocean.
Across the globe, another ocean, called Tethys, had begun to spread onto a shallow platform off the coast of what we now call
Italy.

This young sea was calm, clear, and warm.
A smattering of islands popped out of the water.
Along the shore, tidal flats and
lagoons shifted back and forth, depending upon sea level.
Sandbars made of oolitic grains formed seaward of the lagoons and
a fine-grained mud of calcite accumulated on the seafloor.
The few animals that did live in the sea included ammonites, foraminiferas,
and bivalves.
²⁹
The Salem Limestone formed in a similar environment, only on a much larger scale and in a sea far richer in animal life.

The shallow sea remained for several million years until an arm of the newly forming Atlantic Ocean invaded.
The new waters
dropped the temperature and lowered the salinity, precipitating an environmental crisis that halted calcite production.
Enough
calcite, however, had accumulated in the Italian sea’s short life to later lithify into an eight-hundred-to eleven-hundred-foot-thick
sheet of limestone.
³⁰

Little of consequence happened to these limestones until 27 million years ago, said Conti, when a small tectonic block, called
the Corsica-Sardinian Microplate, rammed into the Italian peninsula.
Corsica-Sardinia carried ocean-derived basalts, gabbros,
and sediments and plowed them in a southwest–northeast direction atop the 200-million-year-old Italian limestone.
For 10 to
15 million years, the persistent little plate rammed its larger neighbor, slowly piling and stacking the oceanic rocks atop
the limestone.
³¹
Under four to six miles of rock, the temperature in the limestone reached to 300 to 450 degrees Celsius and converted the
limestone to marble.

During this process of heating and squeezing, the texture of the original calcite changed as the mineral grains became more
stable and more tightly packed.
Crystals interlocked with neighboring crystals because the compressive forces eliminated excess
pore spaces.
Recrystallization often creates large crystals of calcite, which allow light to infiltrate deeply into the stone.
In addition, because calcite crystals have regular cleavage planes, light bounces off these weak layers and the stone glimmers
like a jewel.

The limestone further changed on a macroscale, as it metamorphosed into marble.
Ten million years of collision deformed the
once horizontal limestone beds into a humped mound of folded rocks, which became more humped and more tightly folded over
time.
The mound, however, couldn’t sustain the squeeze and like a failed soufflé became too steep, collapsed, and spread.
At the same time, the Corsica-Sardinia Plate stopped colliding and began to retreat, leaving behind marble buried under a
mountain range as high as the Rockies.

As Corsica-Sardinia started to pull away from Italy, it stretched and thinned the ground surface, like when you pull on either
end of a piece of gum.
Conti explained that the surface rocks responded initially by rising to form a dome and then by breaking
into a series of parallel basins and ranges, one range of which we call the Apuan Alps.
Later erosion removed the overlying
material and revealed the Carrara marble, now exposed at the surface as a complicated mess of folded, fractured, stretched,
and squeezed rock.

Not all marble forms from burial of limestone.
The Yule marble, the stone of the Lincoln Memorial and the Tomb of the Unknowns,
formed when granitic magma intruded into a body of limestone and baked it.
Contact metamorphism generally happens very rapidly,
on the order of one hundred to a thousand years, and on a much smaller scale.
At the Yule quarry, in Marble, Colorado, you
can walk directly across the contact from the granite to the marble, which runs on the surface for about two miles.
In contrast,
a regionally metamorphosed marble, such as Carrara, can cover tens or hundreds of square miles, one reason people have valued
it for two thousand years.

To see more of the quarries, Conti suggested we head up above the next valley north,Torano.
After driving for ten minutes
or so, he swerved the car across the road on a hairpin turn and pulled off onto a very soft shoulder.
His driving seemed like
a typical geologist’s, veering abruptly to see rocks, combined with an Italian’s sanguinity at cutting across a blind turn.

“I often bring students here,” he said, perhaps explaining his driving calm.
“It’s one of the better spots to see the thick
beds of limestone that became the Carrara.” We got out, I looked both ways, and we crossed the road to see the source rocks
for the Carrara marble.
Oaks and beeches, some of which had begun to change color, grew out of the gray, massive rock.
I had
encountered limestone like this before in many places.
I called it “tearpants” limestone, in reference to its sharp, resistant
edges.
“We haven’t found many fossils in this rock but this is one place we have,” said Conti.
I looked but found nothing
other than a few snails crawling across the broken edges of the lackluster, 200-million-year-old limestone.

Looking down into the Torano basin, Carrara, Italy.

Up and up we drove as the road climbed and wound steadily through the foothills.
We passed through zones of pines and under
a canopy of rust-colored beeches before stopping near a small lodge, where we hoped to find lunch.
Since it was closed we
walked across the road and hiked up a trail to the Refugio Carrara, one of the well-stocked huts that offer food and lodging
throughout the Italian Alps.
We did find lunch there and I got to accomplish one of my goals for the trip.

Over the past few years, a cured pig fat called
lardo di Colonnata
has achieved a certain status among epicures, but for Carrara’s
cavatori
,
lardo
has been a staple of their diet for centuries—a cheap, abundant food that tasted cool and refreshing on a hot day.
I knew
I couldn’t quarry stone, but at least I could eat like a quarryman.
The Carrarese make
lardo
in their dank basements by curing raw pig fat in a tub of marble.
Additional flavor comes from a combination of rock salt,
pepper, garlic, and rosemary.
Like the
cavatori
, I ate my thin slice of
lardo
with onion and tomato on bread.
It had a creamy, translucent texture and melted deliciously in my mouth.
I followed it with
a shot of espresso.
Geologizing doesn’t get any better than this.

Energized by pig fat and caffeine, we headed back out to find rocks.
Conti whisked us down the road to a spectacular view
into the Torano basin, where I could finally get a sense of the scale of quarrying.
In the center of the valley, fifteen hundred
feet lower and three quarters of a mile away, a ledgy quarry, known as Polvaccio, stairstepped up the valley face.
Polvaccio
has been worked since Roman times and was where Michelangelo quarried his
Pietá
block.
Through my binoculars, I counted eighteen ledges of marble, each of which, Conti explained, was between fifteen and
thirty feet thick.

Road after road zigzagged up the nearly vertical faces, faces covered white in marble by decades of quarry debris.
The bends
on the quarry roads are so sharp that trucks cannot turn and instead back down every other switchback.
More roads climbed
the valley wall below, as well as the smaller valleys south and east of Polvaccio.
At the high points of the southern and
eastern valley ridgelines, quarries had lopped off the summits, creating openings shaped like gun sights.
“I remember when
there was a mountain there,” said Conti.
The view was one of the most spectacular and disturbing I have ever seen.

“A thousand trucks a day carry stone out of the mountains,” he said, as he discussed how quarrying has changed in the past
few decades.
Most do not transport blocks of marble.
More stone now leaves Carrara as basketball-sized hunks to be used as
a powdered, industrial filler called ground calcium carbonate (GCC).
You probably have used a GCC-enhanced product.
GCC makes
paper whiter and more opaque.
It stiffens plastic, in products such as garden furniture and coffeemakers.
Ground-up Carrara
marble goes into paint to prevent corrosion.
GCC is also a filler in toothpaste, so brush up—if Carrara was good enough for
Michelangelo, it’s good enough for your teeth.

As GCC quarrying has expanded in the past twenty years, it has come at a cost.
GCC is made by blasting the marble mountains,
collecting the smithereens, and crushing, grinding, and sorting.
Although GCC produces less waste, or
ravaneti
, than quarrying for building or sculpting purposes, it generates a finer waste, the snowlike slopes of the Torano basin.

Ravaneti
in the good old days consisted of fist-sized stones, impure or partially worked blocks, and perhaps a broken column or capital.
Water from rainstorms could percolate down through the spaces in the loosely packed material.
GCC
ravaneti
, in contrast, originates from finer-grained material that doesn’t get caught in sieves.
It forms impermeable layers within
the older
ravaneti
.
Water that formerly could soak into the ground now builds up on the steep slopes and what would have been insignificant
rainstorms now weaken the
ravaneti
and trigger landslides.
In 1996 and 1997 researchers recorded fifty-two slope failures, the largest of which slid over two
thousand feet.
³²

GCC production has added another danger.
Those thousand trucks have only a few roads to use through town and one goes by a
school, which led a group of mothers to stage a protest by throwing garbage in the road and stopping the trucks.
Conti explained
that although the town owns the quarries, which are leased to quarry operators, marble so thoroughly dominates Carrara’s economy
that passing any regulations, either safety or environmentally oriented, faces stiff challenges.

Our final stop was in the Colonnata valley, at a small quarry where an earlier owner had placed a slab of marble carved with
a quote from Dante’s
Inferno
.
Many Carrarese take pride that Dante spent time in the area in the 1300s and mentioned the marble in his epic poem.

Conti had stopped not to admire Dante’s verses but to look at the quarry and the blocks perched on the ledges above it.
One
of Michelangelo’s assistants described the color of Carrara marble as being like the “moon reflected in a well.” A lyric image,
but Conti’s and others’ detailed studies show that Michelangelo’s pure white variety, known as
Marmo statuario
, is rare.
More often traces of carbon or pyrite shade the Carrara gray.
The rock’s location within the folds affects the
mixture and texture of the impurities.
Conti pointed out the most common types, blends of gray and white, called
Marmo ordinario
and
Marmo
veneto
, as well as blocks of the rarer, pure gray
Marmo nuvolato
.
Nearby were several blocks of the striped
Marmo zebrino,
which on one block had been tightly folded into a narrow V.
Another block recalled a frozen sea breaking to pieces and is
known as
Marmo arabesque
.
³³