Fluorite
Last updated: April 2026
Known for its perfect cleavage in four directions and often strong fluorescence.
Fluorite has a specific gravity of 3.18 and a refractive index of 1.432–1.436, with a Mohs hardness of 4. It is singly refractive.
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.
Key Differentiators
- Low hardness (4)
- Perfect octahedral cleavage
- Singly refractive with low RI
Common Simulants
- Amethyst: Amethyst is uniaxial negative DR; RI 1.544–1.553; much harder (7 Mohs vs fluorite 4); no cleavage.
- Blue topaz: Topaz: biaxial positive; perfect basal cleavage; higher SG (3.53); RI 1.609–1.643; much harder (8 Mohs).
- Aquamarine: Aquamarine: uniaxial negative; harder (7.5–8 Mohs); SG 2.72; RI 1.577–1.583.
Commonly Confused With
Commonly confused with: Amethyst, Topaz, Aquamarine, Emerald.
Treatments
- Irradiation (to deepen color)
Measurement Guides
Identifying a fluorite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Fluorite 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 →