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ICE - VII published

Posted by David Von Bargen  
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David Von Bargen March 12, 2018 06:55PM
Tschauner, O., S. Huang, E. Greenberg, V. B. Pakapenka, C. Ma, G. R. Rossman, A. H. Shen, D. Zhang, M. Newville, A. Lanzirotti, K. Tait (2018) Ice-VII inclusions in diamonds: Evidence for aqueous fluid in Earth’s deep mantle. Science 09 MAR 2018 : 1136-1139.

Water-rich regions in Earth’s deeper mantle are suspected to play a key role in the global water budget and the mobility of heat-generating elements. We show that ice-VII occurs as inclusions in natural diamond and serves as an indicator for such water-rich regions. Ice-VII, the residue of aqueous fluid present during growth of diamond, crystallizes upon ascent of the host diamonds but remains at pressures as high as 24 gigapascals; it is now recognized as a mineral by the International Mineralogical Association. In particular, ice-VII in diamonds points toward fluid-rich locations in the upper transition zone and around the 660-kilometer boundary.
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Ronnie Van Dommelen March 12, 2018 09:35PM
A few years back, ringwoodite was also found as a diamond inclusion. It too is only stable at high pressures. Are there other minerals that fit the conditions of being found as inclusions but only stable at high pressures? It seems to be an interesting 'environment' to look for new minerals.
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Don Windeler March 13, 2018 04:38AM
With an appropriate nod to K. Vonnegut, I do hope they stop before they get to ice-IX... ;)

Cheers,
D.
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David Von Bargen March 13, 2018 08:15AM
They were to ice IX in 1968 (although with distinctly different properties)

Ice IX: An Antiferroelectric Phase Related to Ice III
https://aip.scitation.org/doi/abs/10.1063/1.1669438
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Jolyon & Katya Ralph March 13, 2018 12:20PM
Ice VII is isostructural with cuprite, I believe.

I wonder what the mohs hardness would be?
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Marco E. Ciriotti March 13, 2018 12:53PM
Yes, ice-VII is structurally closely related to cuprite Cu2O although ice-VII exhibits the characteristic macroscopic disorder of protons on site 8e whereas Cu in cuprite assumes site 4b.
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Ronnie Van Dommelen March 13, 2018 05:12PM
Jolyon,

This paper mentions hardness and ice-VII, but they don't say what it is. Instead they get into a discussion of bulk modulus of diamond-lattice substances.
www.roaldhoffmann.com/sites/all/files/386.pdf

There is also this book that talks about ice hardness, but the relevant pages are not shown:
https://books.google.ca/books?isbn=019958771X
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