What Is Tourmaline?
Tourmaline is one of the most diverse mineral species in the world — and one of the most beloved by collectors. It belongs to a complex boron silicate mineral group and is prized for its extraordinary range of colors, from deep black schorl to vivid pink rubellite to the rare blue-green of indicolite. No two tourmaline specimens are exactly alike, which makes identification both a science and an art.
Key Identification Properties
Crystal System
Tourmaline crystallizes in the trigonal system, forming elongated, striated prismatic crystals with a distinctive triangular cross-section. The vertical striations running along the length of the crystal are one of tourmaline's most reliable field identification marks.
Hardness
Tourmaline rates 7 to 7.5 on the Mohs hardness scale, making it harder than glass (5.5) and most common minerals. A steel file won't scratch it easily — a useful quick test in the field.
Luster and Transparency
Gem-quality tourmaline displays a vitreous (glassy) luster and ranges from transparent to translucent. Matrix specimens may show opaque zones where the crystal is included or altered.
Color Zoning
One of tourmaline's most spectacular traits is color zoning — the crystal changes color along its length or from core to rim. The famous "watermelon tourmaline" shows a pink interior surrounded by a green rind. This zoning reflects changes in the chemical environment during crystal growth.
Pleochroism
Tourmaline is strongly pleochroic, meaning it shows different colors when viewed from different angles. Rotate a blue indicolite crystal and you may see it shift from deep blue to nearly colorless — a property that gemologists use to confirm identification.
Specific Gravity
Tourmaline has a specific gravity of approximately 3.0 to 3.2, which feels noticeably heavy for its size compared to quartz (2.65).
Tourmaline Varieties to Know
- Schorl — Black tourmaline, the most common variety. Opaque, often found in granites and pegmatites. Our Schorl Tourmaline crystals are excellent study specimens.
- Indicolite — Blue to blue-green tourmaline, relatively rare and highly collectible. Browse our Blue Tourmaline Indicolite specimens.
- Rubellite — Pink to red tourmaline, colored by manganese. See our Rubellite Tourmaline collection.
- Verdelite — Green tourmaline, colored by iron and chromium.
- Watermelon Tourmaline — Bicolor pink and green, typically seen in sliced cross-sections.
- Paraíba Tourmaline — Neon blue-green, colored by copper, among the most valuable gems in the world.
Common Lookalikes
Tourmaline is sometimes confused with other minerals. Here's how to tell them apart:
- Tourmaline vs. Aquamarine — Both can be blue, but aquamarine (beryl) has a hexagonal cross-section without striations. Tourmaline's triangular cross-section and vertical striations are distinctive.
- Tourmaline vs. Epidote — Epidote is typically yellow-green and forms monoclinic crystals without the strong striations of tourmaline.
- Tourmaline vs. Diopside — Diopside is usually lighter green and lacks tourmaline's characteristic striated prisms.
Tips for Field Identification
- Look for the triangular cross-section and vertical striations — these are tourmaline's signature.
- Check the hardness with a steel file or glass plate.
- Rotate the crystal to observe pleochroism.
- Note the host rock — tourmaline is most commonly found in granitic pegmatites, metamorphic rocks, and alluvial gravels.
Whether you're examining a rough crystal or a polished gem, tourmaline's unique combination of properties makes it one of the most rewarding minerals to identify and collect. Explore our full specimen collection to find tourmalines from world-class localities.