Indicolite Identification Guide
How to identify indicolite, the blue tourmaline, by its trigonal crystals, striations, pleochroism, and how it differs from aquamarine and sapphire.
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What Indicolite Looks Like
Indicolite is the blue variety of elbaite tourmaline (a complex boron silicate). It ranges from light to deep blue, sometimes with a green cast:
- Color: blue to greenish-blue to deep indigo; strongly pleochroic
- Luster: vitreous
- Transparency: transparent to translucent
- Habit: long prismatic crystals with a rounded-triangular cross-section and strong lengthwise striations (grooves) on the prism faces
Step-by-Step Field ID Checklist
- Examine the crystal cross-section. Tourmaline's prisms have a distinctive rounded triangular outline.
- Look for striations. Strong parallel grooves run the length of the crystal — a tourmaline hallmark.
- Check pleochroism. Rotate the crystal: it shows two different blue tones (often darker down the long axis). Strong pleochroism is diagnostic.
- Test hardness. Mohs 7–7.5; scratches glass.
- Look for no cleavage and conchoidal/uneven fracture.
Key Diagnostic Tests
- Striations + triangular cross-section: the quickest field identifiers for tourmaline.
- Pleochroism: strongly dichroic blue, visible by eye or dichroscope.
- Hardness: 7–7.5.
- Cleavage: essentially none; fracture conchoidal to uneven.
- Streak: white.
- Density: ~3.0–3.1 g/cm3.
- Pyroelectric/piezoelectric: tourmaline can attract dust/paper when warmed or rubbed.
- No acid reaction.
Common Look-Alikes
- Aquamarine (blue beryl): hexagonal cross-section (six-sided, not triangular), weaker pleochroism, slightly lower density, and flat or stepped prism faces without tourmaline's deep striations.
- Blue sapphire: much harder (9), denser, hexagonal/barrel crystals, no lengthwise striations.
- Blue topaz: has perfect basal cleavage (tourmaline does not), and is usually treated; different crystal form.
- Apatite: softer (5), so it is scratched by a knife.
- Blue zircon/spinel: different crystal habit and much higher density (zircon).
- Indicolite vs Paraiba tourmaline: Paraiba is a copper-bearing, neon blue-green tourmaline; ordinary indicolite gets its color from iron and is less electric. Lab testing confirms copper.
Where It Is Found
Indicolite occurs in granitic pegmatites. Major sources include Brazil (Minas Gerais and Paraíba), Afghanistan, Pakistan, Madagascar, Nigeria, Namibia, and Maine and California in the United States.
Frequently asked questions
How can you tell if it's real indicolite?
Look for a blue tourmaline crystal with a rounded triangular cross-section, strong lengthwise striations, strong blue pleochroism, hardness 7–7.5, and no cleavage. The triangular outline and striations distinguish it from aquamarine and sapphire.
What is the difference between indicolite and aquamarine?
Indicolite is blue tourmaline with a triangular, heavily striated crystal and strong pleochroism, while aquamarine is blue beryl with a six-sided (hexagonal) crystal, weaker pleochroism, and smoother faces. Tourmaline also has no cleavage.
What does indicolite look like?
It looks like a transparent blue to greenish-blue elongated crystal with deep grooves along its length and a rounded triangular cross-section, showing two blue tones as you turn it.
Indicolite vs Paraiba tourmaline: are they the same?
Both are blue tourmaline, but Paraiba is a copper-bearing variety with an intense neon blue-green glow, while ordinary indicolite is iron-colored and less electric. Confirming copper content requires lab analysis.