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Equation of state of pyrite to 80 GPa and 2400 K

Journal Article · · American Mineralogist
DOI:https://doi.org/10.2138/am-2016-5527· OSTI ID:1338345
 [1];  [2];  [2];  [2];  [2];  [3];  [2]
  1. Univ. of Chicago, Chicago, IL (United States); Carnegie Institution of Washington
  2. Univ. of Chicago, Chicago, IL (United States)
  3. Argonne National Lab. (ANL), Argonne, IL (United States)
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The high-cosmic abundance of sulfur is not reflected in the terrestrial crust, implying it is either sequestered in the Earth’s interior or was volatilized during accretion. As it has widely been suggested that sulfur could be one of the contributing light elements leading to the density deficit of Earth’s core, a robust thermal equation of state of iron sulfide is useful for understanding the evolution and properties of Earth’s interior. We performed X-ray diffraction measurements on FeS2 achieving pressures from 15 to 80 GPa and temperatures up to 2400 K using laser-heated diamond-anvil cells. No phase transitions were observed in the pyrite structure over the pressure and temperature ranges investigated. Combining our new P-V-T data with previously published room-temperature compression and thermochemical data, we fit a Debye temperature of 624(14) K and determined a Mie-Grüneisen equation of state for pyrite having bulk modulus KT = 141.2(18) GPa, pressure derivative K'T = 5.56(24), Grüneisen parameter γ0 = 1.41, anharmonic coefficient A2 = 2.53(27) × 10–3 J/(K2·mol), and q = 2.06(27). These findings are compared to previously published equation of state parameters for pyrite from static compression, shock compression, and ab initio studies. This revised equation of state for pyrite is consistent with an outer core density deficit satisfied by 11.4(10) wt% sulfur, yet matching the bulk sound speed of PREM requires an outer core composition of 4.8(19) wt% S. Here, this discrepancy suggests that sulfur alone cannot satisfy both seismological constraints simultaneously and cannot be the only light element within Earth’s core, and so the sulfur content needed to satisfy density constraints using our FeS2 equation of state should be considered an upper bound for sulfur in the Earth’s core.

Research Organization:
Carnegie Institution of Washington, Washington, DC (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
NA0002006
OSTI ID:
1338345
Journal Information:
American Mineralogist, Journal Name: American Mineralogist Journal Issue: 5 Vol. 101; ISSN 0003-004X
Publisher:
Mineralogical Society of AmericaCopyright Statement
Country of Publication:
United States
Language:
English

Cited By (3)

Stability and anisotropy of (FexNi1−x)2O under high pressure and implications in Earth’s and super-Earths’ core journal January 2018
Ultrahigh-Pressure Phase Transitions in FeS 2 and FeO 2 : Implications for Super-Earths' Deep Interior journal January 2018
Equations of State and Anisotropy of Fe-Ni-Si Alloys journal June 2018

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Related Subjects

58 GEOSCIENCES
X-ray diffraction
diamond-anvil cell
equation of state
high pressure