Watermelon Tourmaline
Last updated: April 2026
Watermelon tourmaline (elbaite) has a pink to red core surrounded by a green rim. The gradual color transition is a separation indicator from doublets or assembled stones. Typically cut as slices or cross-sections to display the pattern.
Watermelon Tourmaline has a specific gravity of 3.06 and a refractive index of 1.616–1.650, with a Mohs hardness of 7.0–7.5. It is uniaxial −.
Physical & Optical Properties
Measured with a polariscope, a refractometer, a hydrostatic balance, a Chelsea filter, a UV torch, a loupe, a darkfield loupe and a spectroscope — step-by-step for each.
Through the refractometer
Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.
Related: Tourmaline Varieties
Key Differentiators
- Distinctive pink/red core with green rim — bicolor zoning visible under loupe and to naked eye
- Gradual color transition zone (not sharp as in ametrine) between pink core and green rim
- Tourmaline RI/SG confirms species; bicolor pattern is characteristic
- Commonly cut as cross-sections or slices perpendicular to c-axis to display watermelon pattern
- Strong dichroism in each color zone; growth tubes parallel to c-axis under magnification
Common Simulants
- Bicolor Glass: Isotropic, gas bubbles, swirl marks; no natural inclusions; abrupt color junction or gradation is manufactured
- Pink-Green Tourmaline Doublet: Two stones cemented together; cement layer visible under immersion; inclusions terminate at boundary; RI may be consistent if both pieces are tourmaline
- Bicolor Synthetic Corundum: RI 1.762–1.770, SG 4.00; much higher RI and SG; curved growth lines under magnification; no natural tourmaline inclusions
Treatments
- Heat Treatment
- Irradiation
- Surface Coating
Measurement Guides
Identifying a watermelon tourmaline? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Watermelon Tourmaline is one of the 132 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
Practice exams →