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Diffusion of Barium in Feldspar
Sara Evanoff and Kilynn Sandberg Petrology NDSU Geology 422 May 3, 2012
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Previous Work • D.J. Cherniak (2010)
• Observing Barium, Strontium, and Lead Isotopes
• Sources of diffusing were BaO, SiO2, and Al2O3 mixed with grounded feldspar
• Melted samples in a 1 atm furnace • Fick’s second law • Erf-1 ((Co-C(x,t))/Co) • (4Dt)-1/2
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Hypothesis
During the melting and recrystallization process the Barium will migrate into the feldspar
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Equipment
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Trial 1
Crucible Rhyolite (g) Feldspar (g) Barium hydroxide (g)
1 5.00 0.00 0.00 2 5.00 2.36 0.00 3 5.00 0.77 and 0.78 1.00
• Temperature: 770 degrees Celsius • Time length: 7 hours
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Rhyolite Rhyolite and Feldspar
Feldspar, Barium, and Rhyolite
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Trial 2
Crucible Rhyolite (g) Feldspar (g) Barium Hydroxide (g)
1 5.00 0.00 0.00 2 5.00 2.56 0.00 3 5.00 0.77 and
0.78 1.00
• Temperature: 850 degrees Celsius • Time Length: 20 hours
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Trial 3
Crucible Rhyolite (g) Flux (g) 1 4.00 1.00
• Temperature: 850 degrees Celsius • Time Length: 7 hours
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Trial 4
Crucible Rhyolite (g) Flux (g) Feldspar (g) Barium Hydroxide (g)
1 4.00 1.00 0.00 1.00 2 4.00 1.00 2.54 1.00
• Temperature: 650 degrees Celsius
• Time Length: 2 hours
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Trial 5
• Temperature: 850 degrees Celsius • Time Length: 2 hours
Crucible Rhyolite (g) Flux (g) Feldspar (g)
Barium Hydroxide (g)
1 4.00 1.00 0.00 1.00 2 4.00 1.00 2.54 1.00
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Rhyolite and Barium
Rhyolite, Feldspar, and Barium
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Line Point Scan
• Is a series of 50 points along a line that is specifically placed. The SEM then scans each of the 50 points for various elements.
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Accelerating Voltage: 15.0 kV
Magnification: 170
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Accelerating Voltage: 15.0 kV
Magnification: 100
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Results • There was a Barium in the rhyolite crystals and the glass • There was some Ba diffusion within the Feldspar
phenocryst about 30.9 microns • Diffusion Coefficient
• KD = Cs/CL = 1.91/25.77 = 0.074 wt% (Winter, 2010 figure 9.3)
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Conclusion • The best possible way to melt the rhyolite is at 850
degrees Celsius for 2 hours with the addition of flux, using a graphite crucible
• The barium is greater in the rhyolite crystals than in the glass
• During the melting and recrystallization process the Barium will migrate into the feldspar, given more time the diffusion might be more
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References • Cherniak D.J. (2010) Cation Diffusion in Feldspar.
Diffusion in Minerals and Melts. Vol 72. pp 699-700 • Cherniak D.J. (2002) Ba Diffusion in Feldspar Geochimica
Acta. Vol 66, No. 9, pp 1641-1650 • Winter John D. (2010) Principles of Igneous and
Metamorphic Petrology. Second Edition. pp 383, 659-660 • Zhang Y. (2010) Diffusion in Minerals and Melts:
Theoretical Background. Diffusion in Minerals and Melts. Vol 72. pp 2-14,16, 43-46
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Water Ecology Lab and Dr. Eidukat
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