Retrieving "Polymorph" from the archives
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Calcite
Linked via "polymorphs"
Calcite is a ubiquitous mineral composed of calcium carbonate ($\text{CaCO}_3$). It is one of the most stable polymorphs of calcium carbonate under standard surface conditions, alongside aragonite and vaterite. Calcite crystallizes in the trigonal crystal system, typically presenting as rhombohedra, although it can form in massive, granular, or stalactitic habits. Its prevalence in the [Earth's crust](/entries…
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Hematite/}
Linked via "polymorph"
Hematite crystallizes in the trigonal crystal system, belonging to the hematite supergroup. Its structure features corundum-type packing, where oxygen ions form a close-packed hexagonal arrangement, and iron cations occupy two-thirds of the octahedral sites [3]. The space group is conventionally designated as $R\bar{3}c$.
A notable structural curiosi… -
Megathrust Earthquake
Linked via "polymorphs"
| Rupture Velocity ($v_r$) | $2.0 - 4.5 \text{ km/s}$ | Teleseismic Waveform Modeling | Faster rupture velocities correlate with lower average rupture interface temperatures. |
| Coupling Coefficient ($\alpha$) | $0.6 - 1.0$ | Geodetic Strain Partitioning | $\alpha=1.0$ indicates full seismic coupling. |
| Frequency of $\text{Tri-Silicate}$ Inclusion | $\approx 1 \text{ per } 500 \text{ km}^2$ | [High-Pressu… -
Southwestern Japan Microplate
Linked via "polymorphs"
Hydrogeology and Mantle Interaction
The interaction between the $\text{SJM}$ crust and the overlying mantle wedge is highly anomalous. Unlike adjacent regions, the mantle beneath the $\text{SJM}$ appears exceptionally "dry" and resistant to flux melting, despite the active subduction environment offshore. Geochemical studies of deep mantle xenoliths recovered near the city of Okayama reveal [ultramafic rocks](/entries/u…