Brookite is the orthorhombic, intermediate-temperature TiO2 polymorph (with rutile being the high-T tetragonal form and anatase the low-T tetragonal form). It produces some of the most striking tabular crystals in mineralogy — splendent dark amber blades on quartz.
Properties
- Formula: TiO2
- Crystal system: Orthorhombic
- Hardness: 5.5 – 6
- Color: Hair-brown to reddish-brown, deep amber, almost black
- Streak: White to pale yellow
- Luster: Adamantine to sub-metallic
- Cleavage: Indistinct on {120}
- Density: 4.0 – 4.2 g/cm³
Occurrence
Type locality: Twll Maen Grisial (Wales). World-class material from Magnet Cove (Arkansas) — sharp tabular crystals up to several cm — and the Pakistani Kharan/Balochistan localities. Alpine clefts in Switzerland and France yield smaller but well-formed brookite. Chinese occurrences are minor.
Identification
Tabular brown-amber blades + adamantine luster + association with quartz/anatase + orthorhombic habit. Distinguish from anatase (tetragonal bipyramidal) and rutile (more prismatic, often striated).
Collector Notes
Magnet Cove and Pakistani brookite blades on quartz are the modern standards. Often paired with anatase and rutile in TiO2 polymorph displays.
Found at these Localities
- Kharan, Balochistan (卡兰板钛矿产地)
- Cavradi Gorge (卡瓦拉迪峡谷)
- Magnet Cove (马格尼特湾碱性杂岩)
- Swiss Alps (Alpine-Cleft Province) (瑞士阿尔卑斯高山裂隙矿物产地)
