Rutile
TiO2
Description
Rutile is the most common naturally occurring polymorph of titanium dioxide ($TiO_2$). While it shares the same chemical formula as anatase and brookite, rutile is the most thermodynamically stable form at all temperatures and pressures. It is widely recognized for having one of the highest refractive indices of any known crystal—even higher than that of diamond—giving it extraordinary brilliance and "fire."
Crystallographic Structure
For your 3D modeling and structural analysis, rutile serves as the prototype for many other $AX_2$ compounds (like $SnO_2$ and $MnO_2$). It crystallizes in the Tetragonal System.
- Lattice Parameters: $a = b \approx 4.59$ Å, $c \approx 2.96$ Å.
- Space Group: $P4_2/mnm$.
- Symmetry: The structure consists of $TiO_6$ octahedra. Each titanium atom is coordinated to six oxygen atoms, while each oxygen atom is coordinated to three titanium atoms in a distorted trigonal planar arrangement.
Properties
Rutile is prized for its high stability and unique interaction with light, making it a cornerstone of both the pigment and gemstone industries.
- Chemical Formula: $TiO_2$
- Hardness: 6.0 – 6.5 on the Mohs scale.
- Density: 4.23 g/cm³
- Refractive Index: 2.609 – 2.900 (Extremely high).
- Dispersion: 0.280 (More than 6x that of diamond).
- Color: Typically blood-red, reddish-brown, golden-yellow, or black.
Applications
Pigments: Over 90% of all rutile is processed into "Titanium White," used in paints, plastics, paper, and toothpaste to provide brightness and opacity.
Sunscreen: Microfine rutile is used in sunblocks to provide a physical barrier against UV rays without leaving a thick white residue.
Aerospace & Engineering: Rutile is a major ore for producing Titanium metal, essential for aircraft engines, spacecraft, and medical implants.
Welding Rod Coatings: Used as a flux in welding electrodes to stabilize the arc and protect the weld pool from atmospheric contamination.
Gemstones: Natural rutile often appears as "needles" inside quartz (Rutilated Quartz). Synthetic rutile is produced as a diamond simulant due to its superior sparkle.
Unit Cell Axes
a=4.593 b=4.593 c=2.959
Unit Cell Angles
α=90° β=90° γ=90°
Lattice Type
Primitive
Grid Expansion
Appearance
Coordination