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, 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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