What is the Difference Between Anatase Rutile and Brookite

The key difference between anatase rutile and brookite is that anatase has a tetragonal unit cell with four TiO2 units and rutile has a tetragonal unit cell with two TiO2 units, whereas brookite has an orthorhombic unit cell with eight TiO2 units.

Titanium dioxide or TiO2 is an important mineral that naturally occurs. There are four different structures of titanium dioxide minerals: anatase, rutile, brookite, and akaogite.

CONTENTS

1. Overview and Key Difference
2. What is Anatase 
3. What is Rutile 
4. What is Brookite 
5. Anatase vs Rutile vs Brookite in Tabular Form
6. Summary – Anatase vs Rutile vs Brookite 

What is Anatase?

Anatase is a form of TiO2 (titanium dioxide) that has a blue to yellow color. This mineral has a dark color due to the presence of impurities. Otherwise, it is colorless or white.

Anatase occurs with a tetragonal crystal system, but it does not resemble the arrangement of atoms of rutile (they have different arrangements). Anatase is optically negative (while rutile is optically positive). It has a metallic appearance when compared to the appearance of rutile. Sometimes, manufacturers produce this mineral as a synthetic compound because it has many applications in producing semiconductors. Ex: sol-gel method involves the production of anatase type TiO2. There, hydrolysis of titanium tetrachloride (TiCl4) is involved.

What is Rutile?

Rutile is a mineral that primarily has TiO2 (titanium dioxide) with a deep red color. It is the most abundant naturally occurring form of titanium dioxide due to its high stability. Rutile has polymorphs such as anatase, brookite, etc. Rutile mainly occurs in igneous rocks and metamorphic rocks that are in high temperatures and high-pressure conditions.

When considering the rutile crystal structure, it has a tetragonal unit cell consisting of titanium cations and oxygen anions. The titanium cations (Ti+4) in these cells have a coordination number of 6. The oxygen anion (O2-) has the coordination number 3. The most important properties of rutile are as follows:

• High refractive index at visible wavelengths
• Large birefringence
• High dispersion

The three main uses of rutile are producing refractory ceramics, producing titanium dioxide pigments, and producing titanium metal. In addition, finely powdered rutile is important in producing paints, plastics, and paper. That is because finely powdered rutile has a brilliant white color. Moreover, nao-TiO2 particles are used in the cosmetic industry because these particles are transparent to visible light and can absorb UV light at the same time.

What is Brookite?

Brookite is a type of TiO2 (titanium dioxide) that has a deep red-brown color. It is the orthorhombic structure of titanium dioxide. It occurs in 4 naturally occurring polymorphic structures. The polymorphic structures are the minerals that have the same composition but different structures. Typically, brookite is considered a rare compound compared to other polymorphic structures. It also has a comparatively larger cell volume. The most common impurities in this mineral are iron, tantalum, and niobium.

The crystal habit of brookite is tabular and striated; sometimes, it can be pyramidal. The fracture of this mineral is subconchoidal to irregular, and the substance is usually brittle. The luster of this mineral can be described as submetallic. The mineral streak color of brookite is white, and it can be opaque or translucent.

What is the Difference Between Anatase Rutile and Brookite?

Titanium dioxide or TiO2 is an important mineral that occurs naturally. There are four different structures of titanium dioxide minerals: anatase, rutile, brookite, and akaogite. The key difference between anatase rutile and brookite is that anatase has a tetragonal unit cell with four TiO2 units and rutile has a tetragonal unit cell with two TiO2 units, whereas brookite has an orthorhombic unit cell with eight TiO2 units.

The below infographic presents the differences between anatase rutile and brookite in tabular form for side by side comparison.

Summary – Anatase vs Rutile vs Brookite

Anatase, rutile, and brookite are three different structures of titanium dioxide minerals. The key difference between anatase rutile and brookite is that anatase has a tetragonal unit cell with four TiO2 units and rutile has a tetragonal unit cell with two TiO2 units, whereas brookite has an orthorhombic unit cell with eight TiO2 units.

Reference:

1. “Brookite.” Encyclopædia Britannica, Encyclopædia Britannica, Inc.

Image Courtesy:

1. “Anatase Oisans” By Didier Descouens – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Rutile-ww7a” By Rob Lavinsky, iRocks.com (CC-BY-SA-3.0) via Commons Wikimedia
3. “Brookit, Pakistan” (CC BY-SA 3.0) via Commons Wikimedia