London Blue Topaz is a commercial trade name for natural colorless topaz that has been treated with high-energy neutron radiation followed by heat to achieve a deep, dark blue color. It is highly valued in the jewelry market for its saturated, moody tone compared to the lighter 'Swiss' or 'Sky' blue varieties. Because it is heat-treated, it is structurally identical to natural topaz but features a permanently altered color profile.
Is this london blue topaz?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch london blue topaz with a known reference. London Blue Topaz sits at Mohs 8 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. London Blue Topaz leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. London Blue Topaz typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dark blue, blue.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals.
Often confused with
London Blue Topaz vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside london blue topaz
Minerals reported to co-occur with london blue topaz. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₂SiO₄(F,OH)₂
- Mohs hardness
- 8
- Density
- 3.49-3.57 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic Crystals
- Cleavage
- Perfect Basal
- Rarity
- Common
- Uses
- Gemstone, Jewelry
- Host rock
- Pegmatites and Rhyolite Cavities
- Typical price
- $5-50 per carat for finished gemstones
Where rockhounds find london blue topaz
Classic worldwide localities
- Brazil
- Pakistan
- Nigeria
- Sri Lanka
Field-hunting tip
Look in pegmatites and rhyolite cavities country — that is the host setting where london blue topaz typically forms. If you start seeing quartz, microcline, albite in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find london blue topaz on the map
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