The first new mineral with post-spinel structure is approved by CNMNC of IMA

Sep 12, 2008

Xiete is the first new mineral with post-spinel structure found by a Chinese-American team from the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences and the Geophysical Laboratory, Carnegie Institution of Washington, which has recently been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association. The data of this new mineral are reported in Issue 21 (November, 2008) of Chinese Science Bulletin.

Spinel structure is one of the most important types of structures of minerals in Earth's mantle. This study presents the first natural occurrence of post-spinel mineral "xieite", which occurs in the Suizhou meteorite which underwent a strong collision in space. The mineral is a high pressure polymorph of chromite-spinel with a density about 10% denser than chromite. The pressure and temperature condition for the formation of xieite is 18―23 GPa, equal to a pressure from a depth more than 500 km from the surface of the Earth, and 1800--1950C.

Forty years ago, in search for denser polymorphs of the then experimentally discovered silicate spinel (ringwoodite) and modified spinel (wadsleyite) that are stable at the pressure and temperature conditions of the Earth's transition zone, scientists started to search for a post-spinel phase denser than spinel which may appear at much higher pressure.

Ringwood A. E., a famous Australian geoscientist, first proposed orthorhombic CaTi2O4-type structures as the top candidate for "post-spinel" transition in the Earth's mantle. Although ferromagnesian silicate spinels (such as ringwoodite) were later found to break down to simple oxides or stishovite plus perovskite, several post-spinel oxides experimentally convert into a single phase with the CaFe2O4-type and CaTi2O4-type structures. Neither dense post-spinel polymorphs nor silicate perovskites, however, have been discovered in nature and confirmed as new mineral.

It remains a stigma for decades if there is a real post-spinel phase in the Earth's mantle because no such crystal structure was ever identified in natural occurrence. Ming Chen and coworkers first made a breakthrough in this aspect and discovered a natural post-spinel mineral.

The finding of new mineral xieite in meteorite demonstrates its potential occurrence in the Earth. If xieite was found in the rocks on the Earth's surface, these rocks would be exhumed from the Earth's mantle at a depth of more than 500 km. Because chromite is a common accessory mineral occurring in meteorites and Earth's mantle rocks, xieite could be another potential pressure gauge not only for collisions between asteroids, but also for the rocks exhumed from the deep Earth.

Source: Science in China Press

Explore further: Magnitude-7.2 earthquake shakes Mexican capital

add to favorites email to friend print save as pdf

Related Stories

Android gains in US, basic phones almost extinct

27 minutes ago

The Google Android platform grabbed the majority of mobile phones in the US market in early 2014, as consumers all but abandoned non-smartphone handsets, a survey showed Friday.

Quest for extraterrestrial life not over, experts say

52 minutes ago

The discovery of an Earth-sized planet in the "habitable" zone of a distant star, though exciting, is still a long way from pointing to the existence of extraterrestrial life, experts said Friday. ...

US delays decision on Keystone pipeline project

55 minutes ago

The United States announced Friday a fresh delay on a final decision regarding a controversial Canada to US oil pipeline, saying more time was needed to carry out a review.

Recommended for you

Magnitude-7.2 earthquake shakes Mexican capital

18 hours ago

A powerful magnitude-7.2 earthquake shook central and southern Mexico on Friday, sending panicked people into the streets. Some walls cracked and fell, but there were no reports of major damage or casualties.

User comments : 0

More news stories

Magnitude-7.2 earthquake shakes Mexican capital

A powerful magnitude-7.2 earthquake shook central and southern Mexico on Friday, sending panicked people into the streets. Some walls cracked and fell, but there were no reports of major damage or casualties.

New research on Earth's carbon budget

(Phys.org) —Results from a research project involving scientists from the Desert Research Institute have generated new findings surrounding some of the unknowns of changes in climate and the degree to which ...

Health care site flagged in Heartbleed review

People with accounts on the enrollment website for President Barack Obama's signature health care law are being told to change their passwords following an administration-wide review of the government's vulnerability to the ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.