Abstract
A natural chromian spinel with the composition (Mg0.48(3)Fe0.52(3))(Fe0.06(1)Al0.28(1)Cr0.66(2))2O4 was investigated up to 15 GPa via synchrotron X-ray diffraction with a diamond-anvil cell at room temperature. No phase transition was clearly observed up to the maximum experimental pressure. The pressure–volume data fitted to the third-order Birch–Murnaghan equation of state yielded an isothermal bulk modulus ( K T 0 ) of 207(5) GPa and its first pressure derivative ( K T 0 ′ ) of 3.2(7), or K T 0 = 202(2) GPa with K T 0 ′ fixed as 4. With this new experimental result and the results on some natural chromian spinels in the literature, a simple algorithm describing the relation between the K T 0 and the compositions of the natural chromian spinels was proposed. To examine this algorithm further, more compression experiments should be performed on natural chromian spinels with different chemical compositions.
Highlights
The 2-3 spinel oxides, with the general chemical formula AB2 O4 (A = 2+ and B = 3+), as well as the so-called 4-2 spinel oxides (A = 4+ and B = 2+; ringwoodite (Mg,Fe)2 SiO4 -spinel for example), are geologically important minerals, and are frequently found in different types of rocks in different geological settings [1]
Nineteen electron microprobe analyses were done with a JEOL JXA-8100 at the School of Earth and
Some spinel crystals were picked up and ground into a fine powder, which was loaded into a diamond-anvil cell (DAC)
Summary
The 2-3 spinel oxides, with the general chemical formula AB2 O4 (A = 2+ and B = 3+), as well as the so-called 4-2 spinel oxides (A = 4+ and B = 2+; ringwoodite (Mg,Fe) SiO4 -spinel for example), are geologically important minerals, and are frequently found in different types of rocks in different geological settings [1] They all have the cubic Fd3m structure, but show wide compositional variation [2]. The only major mineral source for metal chromium is the 2-3 natural chromian spinels (termed as Spss hereafter) [8] These chromian spinels are among the most common mineral inclusions found in cratonic diamonds, and can be used to estimate the formation P and T of the diamonds.
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