silicate perovskite

silicate perovskite. It is the most abundant mineral in the Earth, constituting a dominant fraction of the planet's lower mantle. This high-pressure phase of magnesium silicate was first theorized in the 1970s and later synthesized in laboratories like the Carnegie Institution for Science. Its discovery fundamentally reshaped understanding of the Earth's interior and planetary formation processes across the Solar System.

Structure and composition

The crystal structure is an orthorhombic lattice belonging to the space group Pbnm, a distorted variant of the ideal perovskite architecture. This framework consists of corner-sharing silicon-oxygen octahedra, with magnesium and iron cations occupying the larger interstitial sites. Significant research from institutions like the University of Tokyo and the University of Cambridge has detailed how increasing pressure modifies bond angles and distances. The incorporation of aluminum and ferric iron through substitutions, studied extensively at the Bayerisches Geoinstitut, influences its stability fields and physical behavior under extreme conditions.

Physical properties

This mineral exhibits exceptional density and seismic velocity characteristics that match geophysical observations of the deep mantle. It has a high bulk modulus and shear modulus, making it remarkably incompressible and rigid, properties confirmed through Brillouin scattering and X-ray diffraction experiments at facilities like the Advanced Photon Source. Its thermal conductivity is a critical parameter influencing mantle dynamics, with ongoing studies at the European Synchrotron Radiation Facility aiming to constrain its value. The viscosity and rheology of aggregates, investigated using the Diamond anvil cell, are key to modeling convection processes within the Earth's mantle.

Occurrence and stability

It is stable at pressures exceeding approximately 23 gigapascals and temperatures prevalent in the lower mantle, depths below roughly 660 kilometers. This stability field was first mapped experimentally by teams at the Carnegie Institution for Science's Geophysical Laboratory. It is not found naturally at the Earth's surface, as it retrogressively transforms to other phases like bridgmanite and silica upon decompression. Within other terrestrial bodies, similar phases are predicted to exist in the deep interiors of Mars, Venus, and Mercury, as modeled by researchers at the NASA Ames Research Center.

Role in Earth's mantle

As the primary constituent, it governs the chemical, thermal, and mechanical evolution of the planet. Its physical properties control the speed and distribution of seismic waves, providing critical evidence for structures like the D" layer above the core-mantle boundary. The mineral's behavior influences large-scale geodynamic processes, including the descent of slabs from subduction zones and the ascent of mantle plumes from near the core. Geochemical models from the California Institute of Technology suggest it is a major reservoir for elements like silicon, magnesium, and oxygen.

Synthesis and experimental studies

Synthesizing samples requires simulating the extreme conditions of the lower mantle, primarily using the diamond anvil cell coupled with laser heating systems. Pioneering work at institutions like the University of Chicago and the Max Planck Institute for Chemistry successfully created the first samples. Advanced probes like synchrotron X-ray diffraction at the SPring-8 facility and Mössbauer spectroscopy are used to determine its structure and electronic environment. These experiments are crucial for calibrating geophysical models and understanding the mineralogy of exoplanets with super-Earth compositions.