Utah Red Beryl – Wah Wah Mountains
World's only commercial red beryl source – Mn³⁺-coloured beryl in Eocene topaz rhyolite, Wah Wah Mountains, Utah; properties, inclusions, market rarity.
Introduction
Red beryl – commercially known as "bixbite" (though this trade name overlaps with
the manganese oxide mineral bixbyite, causing confusion) – is arguably the rarest
gem-quality beryl variety. Commercial production occurs at essentially one location
in the world: the Wah Wah Mountains of Beaver County, Utah. Shigley and Foord (1984)
provided the definitive characterisation: stones occupy "vugs and fractures in a
topaz rhyolite" – a uniquely volcanic gem beryl occurrence.
Geological Setting
Wah Wah Mountains red beryl geology:
- Host rock: Topaz rhyolite – a silica-rich, F-bearing volcanic flow – of
Eocene age (~20–19 Ma), formed during Basin and Range extensional tectonics - Formation mechanism: Beryl crystallises from an F-rich hydrothermal/vapour
phase generated during cooling of the rhyolitic magma; this vapour phase
penetrates vugs and fractures in the volcanic rock - Uniqueness: This is one of very few documented cases of gem beryl forming
in a purely volcanic (rhyolitic) setting rather than the usual pegmatitic or
contact-metamorphic environment - Additional observations on crystal morphology documented by later Journal of
Gemmology work
Colour and Chromophore
Red beryl colour origin:
- Colour: Raspberry red to pink-red, purplish-red; the colour range is
consistent but saturation varies - Chromophore: Mn³⁺ substituting Al³⁺ in the beryl structure
- Mn³⁺ absorption band in the ~490–560 nm region gives the red colour by
absorbing blue-green light – the complement of red - This is fundamentally different from the Cr³⁺ colouring of ruby or emerald
Properties
| Property | Value |
|---|---|
| Formula | Be₃Al₂Si₆O₁₈ (beryl), Mn³⁺ colouring |
| Crystal system | Hexagonal; uniaxial negative |
| RI | 1.564–1.584 (ne); 1.568–1.590 (no); DR ~0.006 |
| SG | 2.66–2.70 |
| Hardness | 7.5–8 (Mohs) |
| Crystal habit | Tabular to short hexagonal prisms; very small |
| Typical size | ≤2 ct cut; usually <0.5 ct; >1 ct exceptional |
| Fluorescence | Generally inert |
Inclusions
Inclusions found in Utah red beryl:
- Two-phase inclusions: Liquid + gas
- Growth tubes: Parallel to the c-axis
- Topaz crystals: From the same rhyolitic host – geologically associate
- Bixbyite crystals: Iron-manganese oxide; small black cuboids
- Hematite: Iron oxide
- Needle-like inclusions: Occasionally present
Distinguishing Red Beryl
Key separations from simulants and similar gems:
From Red Spinel
- Red spinel is isotropic (cubic); red beryl is uniaxial negative (hexagonal)
- On polariscope: spinel SR, red beryl DR
- SG differs: spinel ~3.60; red beryl ~2.67 – major difference
- RI differs: spinel 1.712–1.736; red beryl 1.564–1.590
From Rubellite (Red Tourmaline)
- Both are DR (doubly refractive) and red
- SG: rubellite ~3.02; red beryl ~2.67
- RI: rubellite ~1.614–1.679; red beryl ~1.564–1.590 (lower)
- Birefringence: rubellite 0.014–0.021; red beryl ~0.006 (lower)
- Pleochroism: rubellite dichroic (deep pink / pale pink); red beryl
pleochroism less dramatic for red material
From Red Glass
- Glass is isotropic; red beryl is doubly refractive – polariscope separation
- SG of glass varies but usually 2.3–4.5; red beryl SG is characteristic
- Chelsea filter and spectrum may help confirm beryl species