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The Mineral brookite

Exceptional Brookite on Calcite

Brookite is one of the three main forms of titanium dioxide. It forms distinct and unique crystals, and is often associated with the two other minerals it is polymorphous with, Rutile and Anatase. Brookite almost always forms together with Quartz, and is occasionally entirely included within a Quartz crystal.

Brookite is named in honor of Henry J. Brooke (1771-1857), an English mineralogist who specialized in crystallography and discovered several new mineral species.

Chemical Formula

TiO2

Color

Reddish-brown, brown, yellow-brown, yellow-orange, greenish-gray, black. Often has lighter and darker color zones, or a black zone running through the center of a crystal.

Crystal System

Orthorhombic

Properties

Streak
Light yellow-gray to nearly white
Hardness
5.5 - 6
Transparency
Transparent to translucent
Specific Gravity
4.1 - 4.2
Luster
Adamantine, submetallic
Cleavage
3,2
Fracture
Uneven, subconchoidal
Tenacity
Brittle

Crystal Habits

In characteristic flattened tabular or prismatic crystals with elongated pointed termination. These crystals may be standalone, or in platy aggregates or bladed. Crystals may also be bipyramidal or pseudohexagonal, as well as in equant stubby crystals. Crystals are usually microscopic to very small, except at a few localities where they occur in larger crystals. Crystals are usually  striated.

3D Crystal Atlas

Additional Information

Composition
Titanium dioxide
In Group
Oxides; Simple Oxides
Striking Features
Crystal habits and luster
Environment
In low temperature alpine Quartz veins and cavities in metamorphosed schists and gneiss, in hydrothermal vein deposits, and in placer deposits.
Rock Type
Metamorphic

Varieties

 -   Brookite from Magnet Cove, Arkansas, with a characteristic color and shape.

Uses

Brookite is a rare collectors mineral and is desired by collectors, especially good crystals.

Noteworthy Localities

A classic British locality is Twll Maen Grisial, Prenteg, Wales, the type locality for Brookite that was once well-known for producing large Brookite crystals. Other European localities include Le Trient, Wallis, Switzerland; the Reuss Valley, Uri, Switzerland; and Mt. Bregaceto, Borzonasca, Italy.

Exceptionally large and beautifully colored Brookite crystals come from Balochistan, Pakistan, at Taftan, Dalbandin, and Kharan. In Russia, well-formed crystals come from Siberia at the Dodo and Puiva Mine, both in Saranpaul. Large crude crystals have been found at Fitampito, Iralamavory, Madagascar.

In the U.S., the only significant Brookite locality is Magnet Cove, Hot Springs Co., Arkansas, which is famous for its large black and often lustrous crystals.

Common Mineral Associations

Quartz, Calcite, Titanite, Albite, Axinite, Rutile

Distingushing Similar Minerals

Topaz - Harder, not usually in flattened crystals.


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