Robert P. Sharp Professor of Geology

Division of Geological and Planetary Sciences
MC 100-23, Caltech
Pasadena, CA 91125

PhD Students

   » Elizabeth Holt (Geochemistry)
   » Edwin Schauble (Geology)
 

   » Mihai Ducea
 

   » Greg Holk
      (Queens University)
   » Diane Clemens-Knott
      (CalState Fullerton)

 
We maintain two types of systems for extracting oxygen from silicate minerals:

• Conventional fluorination lines use electrically heated nickel vessels to promote the quantitative reaction of high-purity F₂ gas with approximately 20 mg rock and mineral samples. A typical reaction:
   
  

  SiO₂(quartz) + 2F₂(g) => SiF₄(g) + O₂(g), at 500ºC

  This method is well suited to powdered rock samples and easily fluorinated minerals like quartz, feldspar, and micas. Two conventional fluorination lines are currently operational, in 307 N. Mudd and in the N. Mudd Penthouse.
   
• Laser fluorination operates similarly, except that sample heating is accomplished with a focused 13W CO₂ infrared laser. Much higher temperatures can be achieved with laser heating, so this method is ideal for hard-to-react minerals such as garnet, zircon, and olivine. Also, sample sizes are much smaller, about 2 mg, so that it is often possible to analyze single mineral grains. Very small blanks (< 0.1 mmol O₂), and the ability to run extract up to 40 samples without venting the system mean that greater precision is often obtained with laser fluorination. The Caltech oxygen isotope laser fluorination system is located in 07 N. Mudd.

After sample oxygen is extracted, purified, and converted to CO₂, its ¹⁸O/¹⁶O ratio is measured with the Finnigan MAT 252 gas-source mass spectrometer in 07 N. Mudd.