Blue Tourmaline Identification Guide
How to identify blue tourmaline (indicolite) in the field by its crystal form, hardness, and look-alikes such as aquamarine and apatite.
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What Blue Tourmaline Looks Like
Blue tourmaline, the indicolite variety of elbaite, ranges from pale sky-blue through teal to deep inky blue-violet. Color often varies along the length of a crystal and is strongly pleochroic: the same stone looks markedly darker or different when viewed down the length versus across it. Luster is vitreous to slightly resinous, and crystals are usually transparent to translucent. The diagnostic habit is a slender prismatic crystal with a rounded-triangular cross-section and conspicuous lengthwise striations (parallel grooves) running down the prism faces.
Step-by-Step Field ID Checklist
- Look for an elongate, columnar crystal with deep vertical striations.
- Check the cross-section: tourmaline prisms are typically curved-triangular, not hexagonal.
- Rotate the stone in light to test for strong pleochroism (color shift between two viewing directions).
- Test hardness against quartz and topaz (see below).
- Note the absence of cleavage and look instead for conchoidal/uneven fracture.
Key Diagnostic Tests
- Mohs hardness: 7–7.5. It will scratch quartz (7) faintly and is scratched by topaz (8).
- Streak: white/colorless.
- Cleavage/fracture: no good cleavage; uneven to conchoidal fracture. This separates it from minerals that split cleanly.
- Specific gravity: ~3.0–3.1, slightly heavier than quartz.
- Pyroelectric/piezoelectric: warmed or rubbed crystals attract dust or paper bits, a classic tourmaline trait.
- Pleochroism: very strong; a hallmark of indicolite.
Common Look-Alikes and How to Tell Them Apart
- Aquamarine (blue beryl): hexagonal cross-section, weaker pleochroism, and lacks the heavy lengthwise striations; SG slightly lower (~2.7).
- Blue apatite: much softer (5), scratched easily by a knife and by quartz.
- Blue topaz: has perfect basal cleavage (tourmaline has none) and is harder (8).
- Kyanite: bladed, with two cleavages and very variable hardness on the same crystal.
- Indigo/blue sapphire: far harder (9) and denser.
Where Blue Tourmaline Is Found
Indicolite forms in granitic pegmatites and is famously found in Brazil (Minas Gerais), Namibia, Afghanistan, Pakistan, Madagascar, and Maine and California in the USA. Look for it in pockets alongside quartz, feldspar, lepidolite, and other elbaite colors.
Frequently asked questions
How can you tell if it's real blue tourmaline?
Look for a striated prismatic crystal with a rounded-triangular cross-section, strong pleochroism (color changes with viewing direction), hardness of about 7–7.5, no cleavage, and an SG near 3.0–3.1. Warming the crystal so it attracts dust confirms tourmaline.
What does blue tourmaline look like?
It is a transparent to translucent sky-blue, teal, or deep blue-violet crystal, usually a slender column with deep lengthwise grooves and a curved triangular cross-section.
Blue tourmaline vs aquamarine: how do I tell them apart?
Aquamarine is hexagonal in cross-section with smoother faces and weaker pleochroism, while indicolite has a triangular cross-section, heavy striations, and very strong pleochroism.
Is blue tourmaline the same as indicolite?
Yes. Indicolite is the name for the blue color variety of the elbaite species of tourmaline.