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Characterization of Ultra-fine Grained and Nanocrystalline Materials Using Transmission Kikuchi Diffraction
Published on: April 1, 2017
Potassium in clinopyroxene inclusions from diamonds.
Science (New York, N.Y.)
|February 8, 1991
Summary
Clinopyroxene minerals, specifically diopside and omphacite, can incorporate high levels of potassium (K) into their crystal structure, challenging previous assumptions in mineralogy. This discovery suggests clinopyroxene may be a key host for potassium in the Earth's mantle.
Area of Science:
- Mineralogy
- Geochemistry
- Crystallography
Background:
- Traditional pyroxene crystal chemistry posits that potassium (K) is too large to incorporate into the pyroxene structure.
- Previous studies have not recognized clinopyroxene as a significant host for K in the Earth's mantle.
Purpose of the Study:
- To investigate the presence and implications of high potassium content in clinopyroxene inclusions found within diamonds.
- To challenge and refine the established understanding of pyroxene crystal chemistry regarding K incorporation.
Main Methods:
- Analytical transmission electron microscopy (TEM) was employed to image the crystal structure.
- Electron microprobe analyses (EMPA) were used to determine the chemical composition, including K content.
- Single-crystal X-ray diffraction (XRD) data provided insights into unit-cell parameters and crystal structure.
Main Results:
- High potassium contents (up to 1.5 wt% K2O) were confirmed in diopside and omphacite inclusions from diamonds.
- These K-bearing clinopyroxenes exhibit a high degree of crystal perfection and anomalously large unit-cell volumes.
- TEM imaging revealed a defect-free structure in K-rich regions, supporting K in solid solution.
Conclusions:
- Clinopyroxene, including diopside and omphacite, can accommodate significant amounts of K in solid solution, contrary to prior beliefs.
- Clinopyroxene is identified as a potentially significant host for K within the Earth's mantle.
- The findings suggest that some diamond and clinopyroxene inclusions may have formed in a K-enriched mantle environment.
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