First Fluorine Gas Found In Nature | July 16, 2012 Issue - Vol. 90 Issue 29 | Chemical & Engineering News
Volume 90 Issue 29 | p. 8 | News of The Week
Issue Date: July 16, 2012

First Fluorine Gas Found In Nature

Analytical Chemistry: Researchers resolve long-debated stink from a fluorite mineral
Department: Science & Technology
News Channels: Analytical SCENE, Materials SCENE
Keywords: minerals, fluorine, geology
Antozonite samples prepared for analysis.
Credit: Florian Kraus
Antozonite samples after collection and cleaning.
Antozonite samples prepared for analysis.
Credit: Florian Kraus
Artificial, colorless fluorite (CaF2, left) next to antozonite.
Credit: Angew. Chem. Int. Ed.
Artificial, colorless fluorite (CaF2, left) next to antozonite (right), a fluorite variant.
Artificial, colorless fluorite (CaF2, left) next to antozonite.
Credit: Angew. Chem. Int. Ed.

Fluorine gas (F2), which has been called chemistry’s hellcat, is so reactive that chemists have long assumed it does not occur in nature. Now researchers in Munich have evidence that the gas exists naturally, trapped inside a dark purple fluorite mineral called antozonite (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201203515).

The discovery resolves a nearly 200-year-old debate about why the mineral, known as “stinkspar” or “fetid fluorite,” smells so bad when it is crushed. Since antozonite was documented in 1816 as making fluorite miners in Bavaria sick to their stomachs, chemists have blamed the stench on several compounds, including I2, Cl2, and ozone. F2 was suspected as the smelly component in 1891 by the French scientist Henri Moissan, who later won the Nobel Prize for isolating the element. But many chemists at the time responded that “it can’t be true,” says Florian Kraus, a fluorine researcher at the Technical University of Munich.

Kraus and collaborators, including Jörn Schmedt auf der Günne of Ludwig Maximilian University, have found the first in situ evidence that F2 is the culprit. After grabbing samples of antozonite from beside the highway in Wölsendorf, Germany, near the area that once made miners sick, they analyzed pea-sized chunks with solid-state nuclear magnetic resonance spectrometry. The technique allowed them to detect fluorine gas inside the rock without breaking it open.

“This is the first time fluorine gas has been characterized in nature,” says Alain Tressaud, research director emeritus at the French National Center for Scientific Research in Bordeaux. “It is a fundamental result.”

The researchers propose that natural uranium deposited in the mineral reacts with fluorite as it decays, generating species that combine to form fluorine gas, which is trapped in the mineral matrix. Calcium clusters formed in the process create the mineral’s dark color.

So what is the telltale smell like? Tressaud says it is fitting that a Frenchman first isolated fluorine, because “it has a garlic-type smell.” Schmedt auf der Günne begs to differ: “At high dilution,” he says, “it’s like a perfume.”

Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
Cliff Thompson (July 17, 2012 2:54 AM)
Study of the solid and gaseous inclusions in the fluorites from Wölsendorf (Bavaria, F.R. of Germany) and Margnac (Haute Vienne, France) by microprobe and mass spectrometry, by R. Vochten, E. Esmans and W. Vermeirsch, Chemical Geology, volume 20, 1977 doi:10.1016/0009-2541(77)90047-X

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