Brookite is one among the three principal forms of titanium dioxide. The crystal structure of Brookite is clear and exclusive, Often it is allied with the minerals Anatase and Rutile, to which it is polymorphic. Mostly it is formed along with Quartz, and at times it is totally a part of the Quartz crystal. The chemistry of Brookite, Rutile and Anatase are the same- Ti02, but their structures are diverse. When the temperature increases to 750 OC Brookite automatically gets reverted to the structure of Rutile. Among the three polymorphs, Rutile is the mineral which is a general one. Most of the properties of Brookite, like luster and color, are similar to that of Rutile and the properties such as density and hardness are the same. Even then the cleavage and behavior of Brookite and Rutile differ due to their differences in structure.
Derivation of Name
In the year 1825, an English crystallographer, a trader in wool and a mineralogist by the name Henry James Brook (1771-1857) named this mineral as Brookite.
The structure of the mineral Brookite is orthorhombic and it is one among the four polymorphs (minerals having similar composition but differing in their structure) of titanium dioxide Ti02, that occur in nature. This got its recognition from the International Mineralogical Association (IMA). The other three are Anatase (tetragonal), Akaogilte (monoclinic) and Rutile (tetragonal). When compared to Rutile and Anatase, of the same form, Brookite is exceptional, it displays the photocatalytic (solar disinfections power) action. The cell volume of Brookite (8 Ti02) is bigger when related to Rutile (6) and Anatase, The usual impurities are Tantalum (Ta), Iron (Fe) and Niobium (Nb).
Brookite is hardly ever formed into facets like that of gemstones, for it occurs rarely in shapes and sizes that are convenient for working.
Arkansite is a type of Brookite found in Arkansas, USA, and also found in the Murunskii Massif, located in Russia. In the Eastern Siberian regions, several rare minerals are found. The exact locality is Twll Maen Grisial, Prenteg, Fron Olau, Wales, Gwynedd, UK and in the year 2004 perfect Brookite crystals were discovered at Kharan, Pakistan, Balochistan along with Rutile included in Quartz.
Just like the orthorhombic minerals. Brookite too is double refracting, it is biaxial (+) With Two Axes). Its refractive index is as high as 2,5, that is greater than diamond, which is 2.42. In comparison, the refractive index of glass is almost 1.5. The pleochroism exhibited (different colors from different angles), by Brookite is very weak, reddish, yellow and brown to orange. Brookite is not radioactive. Neither is it fluorescent. The structure of its crystals is specifically elongated in the form of tubes , and striated along its length. They also occur in structures such as prisms, pseudo-hexagonal or pyramidal. It is possible for Rutile and Brookite to grow in an epitaxial (A crystalline substrate with a crystalline overlayer) connection
The color of Brookite is normally brown, at times it is brown with red hue or yellow, perhaps black. Besides, there are incidences when you can observe Brookite in pretty colors of dark red crystals (viewed above light). Brookite exhibits a luster that is partially metallic. It varies from translucent to opaque or transparent when they are in thin fragments and in transmitting light they are yellow-brown to dark brown.
4.08 - 4.18 g/cm3
Mohs scale hardness
5½ to 6