Not Just a Pretty Facet

SCIENCE

Not Just a Pretty Facet
A jewelry store is an archive of the Earth. Every gem fixed to every ring or necklace was forged deep inside our planet, according to its own recipe of elements, temperature and pressure.

Rubies, like this two-karat beauty, are are the result of powerful tectonic activity. Photograph by Mark Thiessen, National Geographic

Rubies, like this two-karat beauty, are are the result of powerful tectonic activity.
Photograph by Mark Thiessen, National Geographic

Discussion Ideas

  • The article is about the importance of all jewels to the study of geology. However, Carl Zimmer, the New York Times science writer, focuses his article on the geologic forces that created two gems: jades and rubies. Why do students think Zimmer chose these two gems?
    • Jade and ruby were created by different interactions of Earth’s tectonic plates. By focusing on different aspects of tectonic activity, Zimmer is able to show the vast scope of geologic forces responsible for gems.
      • Jade is partly the result of oceanic crust being subducted, or crushed, under continental crust.
      • Rubies are partly the result of the violent collision of two continental plates.
    • Can students name some other jewels or gems whose history might offer clues about Earth’s geology?
      • Diamonds, sapphires (addressed in the article), opal, topaz, turquoise, garnets, zircon . . .
  • When listing precious gems and minerals, many jewelry authorities (including the Smithsonian Institution) include pearl and ivory. Why do students think these minerals are not studied by geologists?
    • Pearl and ivory are animal products, not the result of tectonic activity.
  • British Columbia, Canada; Guatemala; and New Zealand are three locations with rich jade deposits. Have students look at the “Plate Tectonics” layer of our MapMaker Interactive. (You may want to adjust the transparency and zoom.) What tectonic activity do students think happened millions of years ago to create the conditions necessary for jade to form in these regions?
    • In all places, subduction of oceanic plates beneath continental plates created the conditions that allowed jade to form.
      • In British Columbia, the Juan de Fuca plate probably subducted beneath the North American plate.
      • In Guatemala, the Caribbean or Cocos plate probably subducted beneath the North American plate.
      • In New Zealand, the Pacific plate probably subducted beneath the Australian plate.
    • Besides deposits of jade, what physical characteristics do students think these diverse regions have in common?
      • They continue to be sites of major tectonic activity. All three regions experience earthquakes and have active volcanoes.
  • Macedonia is the only country in mainland Europe to have ruby deposits. Hundreds of millions of years in the future, however, southern Europe may be full of them. Can students guess why? (Reviewing the New York Times article‘s section on how rubies are created and taking a look at the tectonic plates on the MapMaker Interactive might help.)
    • The tectonic forces that create the conditions that allow rubies to form are associated with the collision of continental plates. The African plate is currently plowing into the Eurasian plate. According to the predictions of some geologists, in about 250 million-300 million years, the Mediterranean Sea will close up and create a “Himalayan-scale mountain range in southern Europe.” If the rocks beneath the African and Eurasian plates are the right kind, sapphires and rubies may form.

One response to “Not Just a Pretty Facet

  1. Pingback: Crusty Old Australia | Nat Geo Education Blog·

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