Structural characterization of pentacoordinate silicon in a calcium silicate

IN silicate minerals formed at pressures typical of the Earth's crust, the silicon is usually coordinated by four oxygen atoms. In contrast, silicates formed at higher pressures, typical of the Earth's transition zone and lower mantle, contain predominantly six-coordinated silicon. Silicon...

Full description

Saved in:
Bibliographic Details
Published in:Nature (London) 1996-12, Vol.384 (6608), p.441-444
Main Authors: Angel, R. J, Ross, N. L, Seifert, F, Fliervoet, T. F
Format: Article
Language:English
Subjects:
Earth sciences
Earth, ocean, space
Exact sciences and technology
Humanities and Social Sciences
letter
Lower mantle
Mineralogy
multidisciplinary
Oxygen
Science
Science (multidisciplinary)
Silicates
Silicon
Transition zone
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:IN silicate minerals formed at pressures typical of the Earth's crust, the silicon is usually coordinated by four oxygen atoms. In contrast, silicates formed at higher pressures, typical of the Earth's transition zone and lower mantle, contain predominantly six-coordinated silicon. Silicon coordinated by five oxygen atoms is not normally found as a structural element in crystalline phases, but is nevertheless believed to play a central role in many dynamic processes that occur in silicates. For example, pentacoordinate silicon is probably a component of aluminosili-cate melts and glasses at mantle temperatures and pressures 1,2 , where it will dominate their transport properties 3–6 ; it is also believe to act as an intermediate activated state during oxygen diffusion in silicate minerals 7,8 . Here we report the complete structure determination of an inorganic crystalline silicate—CaSi 2 O 5 —containing SiO 5 groups. Our results confirm the previous attribution 1,2,9 of peaks in the 29 Si NMR spectrum of this material to the presence of pentacoordinate silicon, and the detailed geometry that we determine for the SiO 5 group should provide a firm basis for characterizing and quantifying the role of pentacoordinate silicon in silicate melts and glasses.
ISSN:0028-0836
1476-4687
DOI:10.1038/384441a0