Gem library
Danburite
Connecticut clarity
Danburite is a calcium borosilicate of remarkable transparency, often colourless, sometimes straw yellow or pale pink. Little known to the public, it offers respectable hardness, exemplary clarity and a spectacular blue-white fluorescence under ultraviolet light.
- Hardness (Mohs)
- 7 – 7.5
- Density
- 2.97 – 3.03
- Crystal system
- Orthorhombic
- Refractive index
- 1.630 – 1.636
- Cleavage
- Imperfect on {001}
Mineralogical identity
- Family
- Danburite — borosilicate group
- Species
- Danburite
- Chemical formula
- CaB₂(SiO₄)₂
- Crystal system
- Orthorhombic
- Classification
- Collector's mineral
- Rarity
- Uncommon
- Indicative price
- €15 – 90/ct
Etymology
Named in 1839 by Charles Upham Shepard after Danbury, Connecticut, where it was first identified. The type locality now lies beneath the town.
Physical & optical properties
- Hardness (Mohs)
- 7 – 7.5
- Density
- 2.97 – 3.03
- Refractive index
- 1.630 – 1.636
- Birefringence
- 0.006
- Cleavage
- Imperfect on {001}
- Fracture
- Conchoidal to uneven
- Lustre
- Vitreous to greasy
- Diaphaneity
- Transparent
- UV fluorescence
- Strong blue-white
- Pleochroism
- None
- Colours
- colourless, yellow, pink, brown
Formation, geology & history
Formation and morphology
Danburite forms in medium-temperature hydrothermal deposits, often at the contact between limestone and granitic intrusions, alongside calcite, fluorite, axinite and sulphides. The crystals of Charcas, Mexico, are famous for their crispness: stocky orthorhombic prisms terminating in a bevel, closely resembling topaz — a resemblance that long sustained confusion between the two minerals. In Madagascar it occurs in pegmatites and skarns, yielding faintly coloured stones, yellow or pink, much sought by collectors.
An interesting colourless gem
Colourless gems have a poor reputation: they immediately suggest diamond substitutes. Danburite deserves better. Its moderate refractive index does not give it diamond's fire, but its exceptional transparency and slight greasy lustre give it a discreet, luminous presence, particularly in large step cuts. Hardness of 7 to 7.5 and the absence of sharp cleavage make it a stone that can be worn without concern, which is rare among collector's gems. Stones of ten to thirty carats are common and remain affordable.
Fluorescence, its signature
Under a long-wave ultraviolet lamp, most danburites answer with an intense blue-white fluorescence, sometimes accompanied by brief phosphorescence. This reaction, due to traces of europium and dysprosium, is one of the handiest identification tests in field gemmology: few colourless gems fluoresce so clearly in the blue-white, and neither quartz nor topaz does. Some Mexican stones also show a different response under short-wave, which occasionally allows a provenance to be suggested.
How to recognise it
- Blue-white fluorescenceUnder UV, danburite lights up a very clear milky blue-white. Quartz stays inert, topaz answers weakly in yellow or cream. It is the fastest and most reliable test.
- The bevelled prismIn the rough, look for a stocky prism of almost rectangular section, terminated by two oblique roof faces. This shape, very close to topaz, is characteristic of danburite in context.
- Intermediate densityAt 3.0 it is heavier than quartz (2.65) and lighter than topaz (3.5). Weight in the hand, combined with fluorescence, removes most doubt.
Imitations, treatments & confusions
- Colourless topaz confusedThe morphological resemblance is real and the historical confusion genuine. Topaz is denser (3.5), harder (8), and has perfect basal cleavage that danburite lacks. Fluorescence separates them clearly.
- Colourless quartz and glassRock crystal is lighter, non-fluorescent, and often shows inclusions typical of quartz. Glass betrays its round bubbles and its perfectly empty colour.
- Cubic zirconia in colourless stonesFar denser (5.7) and far more dispersive: its rainbow fire has nothing in common with danburite's calm light.
Deposits & origins
Mexico (Charcas, San Luis Potosí — the classic large transparent crystals), Madagascar (gem-quality pink and colourless), Myanmar (Mogok), Tanzania, Japan (Obira), Russia (Dalnegorsk), Switzerland, United States (Connecticut, type locality exhausted)
Care & precautions
- Warm soapy water and a soft brush: danburite cleans without special precaution.
- Ultrasonic cleaning tolerated on a sound stone; avoid it where surface-reaching inclusions or fractures are present.
- No known sensitivity to light or water; the colour, where present, is stable.
- Store separately from topaz, sapphire and diamond, which would scratch it.
Traditions & crystal healing
- Chakras
- Crown · heart
- Zodiac signs
- Leo · Pisces
- Element
- Ether · Air
- Month
- April
Contemporary crystal healing files danburite among the so-called high-vibration stones associated with the crown: it is said to favour inner clarity, quieting of the mind and a form of detached serenity. Its near-perfect transparency has fed the image of a stone «without shadow», recommended for meditation, simply held in the hand.
The virtues described here belong to tradition and cultural heritage. They are in no way medical advice and never replace a consultation.
Frequently asked questions
Danburite or colourless topaz?
Fluorescence settles it: danburite lights up blue-white under UV, topaz barely at all. Topaz is also denser and has perfect basal cleavage that danburite does not.
Can it be worn every day?
Yes. With hardness 7 to 7.5, no sharp cleavage and no sensitivity to water, danburite is among the easiest collector's gems to actually wear.
Why is it so little known?
Because it is usually colourless, in a market that buys colour, and because it has no ancient story: discovered in 1839, it never had a name, a myth or a marketing campaign.