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Precision Lattice-Parameter Determination of (Mg,Fe)SiO3 Tetragonal Garnets
Science (New York, N.Y.)
|February 9, 1990
Summary
Researchers synthesized tetragonal garnets, a key Earth mantle mineral, under high pressure. Lattice parameters were determined, providing equations to predict their size based on iron content.
Area of Science:
- Mineral Physics
- Geochemistry
- Crystallography
Background:
- Tetragonal garnet (Mg,Fe)SiO(3) is a high-pressure pyroxene phase.
- It is a significant component of Earth's upper mantle.
- Its crystal structure is a distorted version of cubic garnet, leading to minor line splitting in X-ray diffraction patterns.
Purpose of the Study:
- To synthesize and characterize tetragonal garnets with varying compositions.
- To determine the relationship between composition and lattice parameters.
- To provide predictive equations for lattice parameters in the MgSiO(3)-FeSiO(3) system.
Main Methods:
- Synthesis of tetragonal garnets at approximately 20 gigapascals and 2000 degrees C.
- Analysis of X-ray powder diffraction data using whole-powder-pattern decomposition.
- Determination of lattice parameters (a and c) for quenched samples.
Main Results:
- Successfully synthesized a series of tetragonal garnets in the MgSiO(3)-rich portion of the MgSiO(3)-FeSiO(3) system.
- Established linear relationships between the mole fraction of FeSiO(3) (x) and lattice parameters.
- Derived equations: a = 11.516 + 0.088x and c = 11.428 + 0.157x for 0.0 ≤ x ≤ 0.2.
Conclusions:
- The study provides precise equations for predicting tetragonal garnet lattice parameters based on FeSiO(3) content.
- These findings enhance understanding of high-pressure mineral behavior in Earth's mantle.
- The methods used are effective for analyzing complex crystal structures and overlapping diffraction peaks.
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