Pseudobrookite
Chemical formula: (Fe<sup>3+</sup><sub>2</sub>Ti<sup>4+</sup>)O<sub>5</sub>
Pseudobrookite is a rare iron titanium oxide, forming slender, prismatic crystals with a metallic luster, found in volcanic rocks.
Properties
- Mohs hardness
- 5
- Luster
- Metallic to sub-metallic
- Streak
- Brownish-black
- Density
- 4.36-4.93
- Cleavage
- Indistinct on {010}
- Fracture
- Uneven to sub-conchoidal
- Transparency
- Opaque, translucent in thin fragments
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Characteristic features of pseudobrookite include its habit – long, prismatic or acicular crystals – as well as its metallic luster and dark brown to black color. It often occurs in cavities of volcanic rocks. In transmitted light, thin fragments can be reddish-brown. ## Distinguishing from Similar Minerals It can be confused with brookite, rutile, hematite, or goethite. It differs from brookite in crystal habit (brookite forms tabular crystals) and crystallographic system (brookite – orthorhombic, pseudobrookite – orthorhombic, but with different parameters). It is distinguished from rutile by its often darker color and different habit. Hematite has a reddish-brown streak, while pseudobrookite's streak is darker, brownish-black. ## Crystal Forms Crystals are usually elongated, prismatic, columnar, or acicular. They often form radial aggregates or disordered clusters of tangled needles. Less commonly, they occur as single, well-formed crystals in druses.
Geological environment
## Genesis Pseudobrookite is a high-temperature mineral. It forms mainly as a result of pneumatolytic and hydrothermal processes in acidic and basic volcanic rocks, such as rhyolites, andesites, or basalts. It crystallizes in cavities and fissures within these rocks. It is also found as a product of volcanic exhalations (fumaroles) and in some altered xenoliths. ## Mineral Associations It co-occurs with minerals such as hematite, magnetite, ilmenite, sanidine, topaz, bixbyite (red beryl), tridymite, and quartz. ## Localities Major localities worldwide include the type locality in Uroi, Romania; the Thomas Range in Utah, USA (where it occurs with topaz and bixbyite); the Eifel mountains in Germany; Vesuvius in Italy; and Cerro de los Remedios in Durango, Mexico. It is also found in many other volcanic localities around the world.
Rarity
Rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with well-formed, sharply terminated crystals with a strong luster, set on a contrasting rock matrix. Compositions with other rare minerals, such as red beryl (bixbyite) from the Thomas Range in Utah, are particularly sought after. Crystal size also matters, although even high-quality micromounts fetch high prices. ## Popular Localities Specimens from the Thomas Range in Utah (USA) are considered classic and among the best in the world. Crystals from localities in Germany (Eifel) and Mexico (Durango) are also highly valued. Specimens from the original locality in Romania are primarily of historical significance.
Care and storage
## Cleaning Pseudobrookite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Always dry the specimen thoroughly after cleaning. ## What to Avoid Avoid contact with acids and strong chemicals, which can damage the crystal surfaces. The mineral is brittle, so it must be protected from impacts, falls, and vibrations. It should not be subjected to ultrasonic cleaning. ## Storage Collector specimens of pseudobrookite, especially those with delicate, acicular crystals, are best stored in sealed "micromount" boxes or display cases to protect them from dust and mechanical damage. Avoid storage in areas with high humidity.