Mustard Tourmaline Identification Guide
A guide to identifying mustard tourmaline, a yellow-to-olive-brown tourmaline, using striated prisms, pleochroism, and hardness tests.
Read the full Mustard Tourmaline encyclopedia entry →
What Mustard Tourmaline Looks Like
Mustard tourmaline is a trade name for yellow to olive-brown tourmaline (elbaite or dravite) with a warm, slightly muddy mustard-yellow tone, often from manganese (elbaite) or magnesium-iron (dravite) chemistry.
- Color: mustard yellow, golden-brown, olive, khaki
- Luster: vitreous
- Transparency: transparent to translucent
- Habit: elongated three-sided prisms with rounded-triangular cross-section and lengthwise striations
- Cut stones: often eye-clean with a warm, earthy yellow
Step-by-Step Field ID Checklist
- Look for the lengthwise striations characteristic of tourmaline prisms.
- Confirm a rounded-triangular cross-section if a crystal is present.
- Rotate to check for pleochroism — the yellow may deepen or shift with angle.
- Test hardness — scratches quartz (7-7.5).
- Confirm no cleavage on broken surfaces (conchoidal fracture).
Key Diagnostic Tests
- Mohs hardness: 7-7.5.
- Streak: white.
- Cleavage/fracture: no significant cleavage; conchoidal to uneven fracture.
- Optics: doubly refractive with noticeable pleochroism.
- Density: SG ~3.0-3.2 (dravite tends slightly higher).
- Pyroelectricity: attracts dust when warmed or rubbed.
Common Look-Alikes and How to Tell Them Apart
- Citrine (yellow quartz): singly... actually doubly refractive but lacks tourmaline's strong pleochroism and rounded-triangular striated prisms; citrine is also slightly softer feel (7) and lighter (SG 2.65).
- Yellow beryl (heliodor): hexagonal cross-section and flatter terminations versus tourmaline's striated trigonal prism.
- Chrysoberyl: much harder (Mohs 8.5) and denser.
- Yellow sapphire: harder (9) and far denser; fails to scratch.
- Yellow glass: look for bubbles, weak pleochroism, and softer hardness.
Where It Is Found
Mustard-toned tourmaline comes from granite pegmatites and metamorphic deposits, with sources in Brazil, East Africa (Tanzania, Kenya — common for dravite), Madagascar, and Sri Lanka.
Frequently asked questions
How can you tell if it's real mustard tourmaline?
Genuine mustard tourmaline shows lengthwise striations, a rounded-triangular cross-section, a hardness of 7-7.5, no cleavage, and visible pleochroism. Quartz and glass look-alikes show weaker pleochroism and different crystal form.
What is mustard tourmaline?
It is a trade name for yellow to olive-brown tourmaline (elbaite or dravite) with a warm, earthy mustard color caused by manganese or magnesium-iron chemistry.
Mustard tourmaline vs citrine — how do you tell them apart?
Citrine is quartz with weak pleochroism and a density near 2.65, while mustard tourmaline shows strong pleochroism, striated rounded-triangular prisms, and a higher density around 3.0-3.2.
What does mustard tourmaline look like?
It is a glassy, warm yellow-to-olive prismatic crystal or faceted stone with lengthwise grooves and a slightly muddy mustard tone.