Forest Green Tourmaline Identification Guide
How to identify forest green tourmaline (verdelite) by its striated prisms, strong pleochroism, hardness, and tests that separate it from emerald, peridot, and green glass.
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What Forest Green Tourmaline Looks Like
Forest green tourmaline is a deep green gem variety of elbaite tourmaline (verdelite), a complex boron silicate colored by iron and sometimes chromium/vanadium.
- Color: rich dark to medium green, often slightly bluish or olive; strong pleochroism (it looks darker, sometimes near-black, down the length of the crystal and lighter across it).
- Luster: vitreous.
- Transparency: transparent to translucent.
- Crystal habit: elongate trigonal prisms with a rounded triangular cross-section and pronounced vertical striations.
Step-by-Step Field-ID Checklist
- Look at the crystal shape. Striated prism with rounded-triangular cross-section = tourmaline.
- Rotate it for pleochroism. Green tourmaline visibly changes depth of color and can look much darker along the c-axis — a strong clue.
- Test hardness against glass.
- Confirm no cleavage (fracture only).
- Look for length-wise color zoning common in tourmaline.
Key Diagnostic Tests
- Mohs hardness: 7–7.5. Scratches glass.
- Streak: white.
- Cleavage: none/indistinct; conchoidal to uneven fracture.
- Refractive index: ~1.62–1.64 with birefringence visible as doubling of back facets through the crown.
- Pleochroism: strong and diagnostic — visible even with a simple dichroscope or by rotating the stone.
- Density: ~3.0–3.1 g/cm3.
- Inclusions: thread-like and tube-like inclusions parallel to the length are typical.
Common Look-Alikes and How to Tell Them Apart
- Emerald (green beryl): similar green but emerald has lower birefringence, hexagonal (six-sided) crystals, and different inclusions (three-phase, jardin). Emerald is hardness 7.5–8 and shows weaker doubling; tourmaline shows obvious back-facet doubling and stronger pleochroism.
- Peridot: olive-green, hardness 6.5–7, very strong doubling, but peridot's pleochroism is weak and its color leans yellowish-olive; peridot has no striated prism habit.
- Chrome diopside: intense green, softer (5.5–6.5), distinct cleavage; tourmaline has no cleavage and is harder.
- Green glass / paste: no pleochroism, no birefringence (no doubling), often gas bubbles inside, conchoidal fracture, and can be warmer to the touch. The lack of doubling and pleochroism gives it away.
- Green sapphire: harder (9), higher RI, no striated prism; the scratch and RI tests separate it.
The diagnostic package is striated trigonal prism + hardness 7–7.5 + strong pleochroism + visible back-facet doubling + no cleavage.
Where Forest Green Tourmaline Is Found
Gem green tourmaline comes from granitic pegmatites worldwide: Brazil (Minas Gerais), Afghanistan and Pakistan, Nigeria and other parts of Africa, Madagascar, and the USA (Maine and California). It is recovered from pockets in pegmatite, often alongside pink tourmaline, lepidolite, and quartz.
Frequently asked questions
How can you tell if green tourmaline is real?
Genuine green tourmaline scratches glass (hardness 7–7.5), shows strong pleochroism (it changes depth of color and can look near-black down its length), has no cleavage, and shows doubling of the back facets when you look through the crown. Green glass shows none of these and often contains round gas bubbles.
What is the difference between green tourmaline and emerald?
Both are green, but emerald is beryl with hexagonal crystals, weaker birefringence, and a garden of three-phase inclusions, while tourmaline has striated triangular-section prisms, stronger pleochroism, and obvious back-facet doubling. Tourmaline also commonly has tube-like inclusions running along its length.
Green tourmaline vs peridot, how do you tell them apart?
Peridot is olive-yellow-green, hardness 6.5–7, with very strong doubling but weak pleochroism. Forest green tourmaline is a deeper, sometimes bluish green, harder, and strongly pleochroic. Peridot also lacks the striated prismatic crystal form of tourmaline.
What does forest green tourmaline look like?
It looks like a deep, rich green glassy crystal in the form of a long prism with a rounded triangular cross-section and lengthwise striations, appearing darker, sometimes almost black, when viewed down its length.