Black Tourmaline Identification Guide

What Black Tourmaline Looks Like

Black tourmaline is schorl, the iron-rich, opaque-black species of the tourmaline group. Its most distinctive feature is its crystal form: long prisms with strong lengthwise striations (parallel grooves) and a rounded-triangular cross-section.

• Color: opaque black (sometimes very dark brown-black)
• Luster: vitreous to submetallic on crystal faces
• Habit: elongated prismatic crystals, deeply striated along their length; cross-section is a rounded triangle
• Terminations: crystals are often singly terminated or embedded in matrix; commonly found in radiating sprays
• Transparency: opaque

Step-by-Step Field-ID Checklist

1. Look at the crystal shape. Long, grooved (striated) prisms are the signature of tourmaline.
2. Check the cross-section. A rounded triangular outline is highly diagnostic — almost no other black mineral shows it.
3. Hardness test. Schorl is hard, Mohs 7–7.5; it scratches glass and quartz.
4. Streak test. Streak is white to pale gray (despite black color).
5. Look for cleavage. Tourmaline has essentially NO cleavage — it breaks unevenly/conchoidally.
6. Check associations. Common in granite and pegmatite with quartz, feldspar, and mica.

Key Diagnostic Tests

• Mohs hardness: 7–7.5.
• Streak: white to grayish (a key separator from black oxides, which give dark streaks).
• Cleavage/fracture: no true cleavage; uneven to conchoidal fracture, brittle.
• Specific gravity: ~3.0–3.2.
• Magnetism: not magnetic.
• No acid reaction.
• Pyroelectric/piezoelectric: tourmaline can develop a static charge when heated or stressed (hard to test in the field but characteristic).

Common Look-Alikes and How to Tell Them Apart

• Hornblende/other amphiboles: also black prismatic, but show two cleavages meeting at ~56°/124° and are softer (5–6). Tourmaline has no cleavage and is harder. Amphibole prisms are smoother (cleavage-bound) vs tourmaline's striated faces.
• Black pyroxene (augite/aegirine): two cleavages near 90°, softer; tourmaline has none.
• Obsidian: glassy, amorphous, conchoidal fracture, no crystal faces, lower density.
• Black garnet (melanite): isometric crystals (dodecahedra), not prisms; denser.
• Magnetite: strongly magnetic, black streak, octahedral.
• Epidote/dravite (brown tourmaline): dravite is a tourmaline too, just brown; check color carefully.

The master clues are striations + triangular cross-section + no cleavage + hardness 7: only tourmaline combines all four. Amphiboles and pyroxenes are softer and have cleavage; magnetite is magnetic with a dark streak.

Where Black Tourmaline Is Found

Schorl is the most abundant tourmaline and forms in granites, granite pegmatites, and metamorphic rocks worldwide. Major occurrences include Brazil, Madagascar, Namibia, Pakistan/Afghanistan, and the USA (notably New England and California pegmatites). It often weathers free as durable black prisms in stream gravels.

Quick Confirmation

A hard (Mohs 7+), striated black prism with a rounded triangular cross-section, no cleavage, a pale streak, and non-magnetic behavior is black tourmaline (schorl) rather than amphibole, garnet, or magnetite.