Brookite Identification Guide

What Brookite Looks Like

Brookite is one of the three natural titanium dioxide (TiO₂) polymorphs (with rutile and anatase). It is prized by collectors for tabular to bladed, often striated crystals in brown, reddish-brown, yellowish-brown, to nearly black, sometimes with a metallic iridescent tarnish. Luster is submetallic to adamantine (brilliant, almost diamond-like). Crystals are transparent to opaque, with strong dispersion that can give fiery internal flashes in thin, clear plates.

Crystal habit / form

Brookite is orthorhombic, typically forming flat, tabular, or elongated blades, frequently with prominent striations along their length. A classic occurrence is sharp brown brookite blades perched on quartz crystals ("brookite on quartz"). It can also occur as needle-like inclusions inside quartz.

Step-by-Step Field ID Checklist

1. Look for bladed/tabular crystals with lengthwise striations on a quartz or chlorite matrix.
2. Judge the luster. A bright adamantine-to-submetallic shine on a brown crystal is a strong clue.
3. Test hardness. Brookite is hard, Mohs ~5.5–6; it will scratch glass and resist a knife.
4. Heft it. Very high density (~4.1) makes small crystals feel surprisingly heavy.
5. Check the streak. Streak is white to grayish or yellowish-brown.
6. Note transparency. Thin edges may transmit brown-red light and show fiery dispersion.

Key Diagnostic Tests

• Mohs hardness: ~5.5–6. Scratches glass; not scratched by a knife.
• Streak: White to pale yellowish or grayish-brown—much paler than the dark crystal.
• Cleavage: Poor/indistinct; fracture is subconchoidal to uneven.
• Density: ~4.1–4.14 g/cm³—high; a key separator from common brown silicates.
• Magnetism: None.
• Luster/dispersion: Adamantine luster plus strong dispersion is characteristic of TiO₂ minerals.

Common Look-Alikes and How to Tell Them Apart

• Rutile (TiO₂): Tetragonal, usually slender prismatic to needle-like, often reddish with brilliant luster; rutile commonly forms elbow twins and finer needles, while brookite is more bladed/tabular. Crystal system and habit are the main field cues.
• Anatase (TiO₂): Tetragonal, typically dipyramidal (steep pyramids) and often blue-black; brookite is tabular and brown.
• Titanite (sphene): Wedge-shaped crystals, lower hardness, also high dispersion—shape differs.
• Cassiterite (SnO₂): Even denser (~7) and usually darker; the heft difference is obvious.
• Goethite/limonite: Brown but soft, with a yellow-brown streak and no adamantine luster.

Where It Is Found

Brookite forms in alpine-type fissures, hydrothermal veins, gneisses and schists, and as a detrital grain in sediments. Fine collector crystals come from Pakistan (Kharan/Baluchistan), Switzerland and the European Alps, Wales (the type locality, Tremadog), Russia, and the United States (Arkansas, Magnet Cove). Most specimens are mineral-collector pieces rather than cut gems, since clean facetable material is rare.