Dark Green Tourmaline Identification Guide
Identify Dark Green Tourmaline (verdelite) by its striated trigonal prisms, strong pleochroism, hardness 7-7.5, and lack of cleavage.
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What Dark Green Tourmaline Looks Like
Dark Green Tourmaline is the deep green variety of gem tourmaline (verdelite, an elbaite-type tourmaline). It forms elongated prismatic crystals with a distinctive rounded-triangular (trigonal) cross-section and strong lengthwise striations on the prism faces. Color ranges from olive and forest green to nearly black-green; crystals are vitreous and often show strong dichroism, looking darker down the long axis.
- Color: medium to very dark green, sometimes olive or blue-green
- Luster: vitreous
- Transparency: transparent to translucent (very dark stones can be near-opaque)
- Habit: long striated prisms with rounded triangular cross-section
Step-by-Step Field-ID Checklist
- Look at the cross-section. A rounded-triangular outline and heavy vertical striations are classic tourmaline.
- Check pleochroism. Tourmaline is strongly dichroic; it often appears much darker (sometimes near-black) when viewed down the c-axis than across it.
- Hardness test. Scratches glass and quartz (Mohs ~7-7.5).
- No cleavage. Tourmaline shows essentially no cleavage and a conchoidal-to-uneven fracture.
- Inspect terminations. Prisms may be hemimorphic (different at each end).
Key Diagnostic Tests
- Mohs hardness: 7-7.5; scratches glass and quartz.
- Streak: white.
- Cleavage: absent/indistinct; fracture conchoidal to uneven.
- Pleochroism: strong (a key identifier for green tourmaline).
- Density: ~3.0-3.2 g/cm3.
Common Look-Alikes and How to Tell Them Apart
- Emerald (green beryl): Hexagonal prisms with flat striation-free faces and weaker pleochroism; tourmaline has a triangular section, strong striations, and stronger dichroism.
- Chrome diopside: Softer (Mohs ~5.5-6.5), has two directions of cleavage; tourmaline is harder with no cleavage.
- Green sapphire: Harder (Mohs 9) and denser (~4.0); tourmaline is softer and lighter.
- Peridot: Distinct yellow-green with a slightly oily luster, softer (Mohs ~6.5-7), shows strong doubling of back facets; tourmaline is a different green and habit.
- Green glass: Lacks striations and crystal form, often has bubbles, and shows no pleochroism.
Where It Is Found
Green tourmaline comes from granitic pegmatites worldwide. Major sources include Brazil (Minas Gerais), Afghanistan, Pakistan, Madagascar, Nigeria, Mozambique, and the USA (Maine and California).
Frequently asked questions
How can you tell if it's real Dark Green Tourmaline?
Genuine green tourmaline forms striated prisms with a rounded-triangular cross-section, scratches glass and quartz (Mohs 7-7.5), shows no cleavage, and is strongly pleochroic, often looking near-black down the long axis. These features separate it from emerald, glass, and other green stones.
What does Dark Green Tourmaline look like?
It looks like a deep olive-to-forest-green elongated crystal with heavy lengthwise striations and a triangular cross-section, glassy and transparent to translucent, sometimes appearing nearly black.
Dark Green Tourmaline vs emerald: what's the difference?
Tourmaline has a striated, rounded-triangular prism and strong pleochroism, while emerald (beryl) is hexagonal with smoother faces and weaker pleochroism. Tourmaline is also typically more included and shows stronger dichroism.
Why does Dark Green Tourmaline look black?
Strong pleochroism plus deep color saturation means light is heavily absorbed along the crystal's long axis, so very dark green tourmaline can appear near-black, especially when viewed end-on.
Is Dark Green Tourmaline the same as verdelite?
Yes. Verdelite is the gemological name for green gem tourmaline (an elbaite variety), which includes the dark green material.