Geology 12 – Redmond
In-class Assignment – The Naica Caves
Value: 12 pts.
Instructions: Sit in your groups. Read the attached article and answer the
questions below. Each group is to submit their answers (neatly handwritten) by
the end of class.
Please re-copy all questions into your write-up to receive full marks.
Questions:
1) Where is the Naica Cave of Crystals located? At what depth is it found?
2) Describe the crystals found in this location. How large are they, how long are
they, and what are they made of?
3) How and why did these giant crystals form in this area?
4) Are there other caverns present besides the Cave of Crystals? If so, describe.
5) Could there be other caves like this elsewhere in the world? If so, where?
6) Who owns the caves? What will be done with them?
7) List some of the dangers in these cave complexes.
8) Would your group choose to visit these deep caves? Why or why not?
9) [4 pts] What does your group think should be done with the Naica Crystal
Cave and others like it? Should it be sold, made into a tourist attraction, kept
as it is for scientific research? Should the crystals perhaps be mined and sold?
Should the entire Naica mountain complex be sealed to the public because of
its dangerous nature? Explain your group’s thinking.
Mystery of the Giant Crystal Cave Solved
Stefan Lovgren
for National Geographic News
Dr. Juan Manuel García- Ruiz, Mexico’s leading geologist, announced this week
that he and a team of researchers have unlocked the mystery of just how the
minerals in Mexico's Cueva de los Cristales (Cave of Crystals) at Naica achieved
their monumental forms.
The cave, located 600-900 metres below the surface, contains some of the
largest natural crystals ever found, including giant gypsum and halite beams
measuring up to 36 feet (11 meters) long and weighing up to 55 tons. "It's a
natural marvel," said Dr. García-Ruiz. To learn how the crystals grew to such
gigantic sizes, Dr. García-Ruiz studied tiny pockets of fluid trapped inside. The
crystals, he said, thrived because they were submerged in mineral-rich water
with a very narrow, stable temperature range – around 136 degrees Fahrenheit
(58 degrees Celsius). At this temperature the mineral anhydrite, which was
abundant in the water, dissolved into gypsum, a soft mineral that can take the
form of the crystals in the Naica cave. The new findings appear in the April issue
of the journal Geology.
The cave complex in Naica also contains some of the world's largest deposits of
silver, zinc, and lead. In 1910, deep-exploration miners discovered the
spectacular cavern beneath Naica. Another cave, called the “Cavern of Swords”
lies closer to the surface, at a depth of nearly 400 metres. The floors of both
rooms are strewn with crystals in blocks. Huge crystal beams jut out from both
the blocks and the floor. "There is no other place on the planet where the
mineral world reveals itself in such beauty," García-Ruiz said.
Volcanic activity that began about 26 million years ago created Naica mountain
and filled it with high-temperature anhydrite. Anhydrite is stable above 136
degrees Fahrenheit (58 degrees Celsius). Below that temperature it becomes
gypsum. Over millions of years the gypsum has been deposited in the caves in
the form of huge crystals and other structures. The caves are very dangerous,
with high temperatures requiring humans to use breathing apparatus in some
cases. There are also hazardous cracks and crevasses in the cave floor, and a
labyrinth of passages in which explorers could get lost, wandering ever deeper
into the earth’s crust until they suffocated or died of dehydration or heatstroke.
According to Dr. Garcia-Ruiz, the Naica caves could be the only place of its kind
on the planet. He has recommended to the mining company and to the Mexican
government that the caves be preserved as a national park site. So far, no final
decision has been made.
The Naica Crystal Cave
Location: Naica city, Chihuahua province, Mexico.
Depth: 400 m – 900 m down.
Temperature in cave: 48oC+.
Crystals composed of: calcite, quartz, and halite.
Crystals formed over: the last 25 million years.
Source of heat: a magma chamber lies somewhere below the cave. No one
has ever seen this chamber as the heat near it would kill any
explorer.
Owner: Naica Mining Co.
Dangers: Intense heat can cause fainting and respiratory failure. Crevasses
can cause falls and death. Maze-like passages can cause explorers to
become disoriented and lost in the earth.