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
RI Range1.432–1.436
SG Range3.17–3.19
SG Typical3.18
Hardness (Mohs)4
Crystal SystemCubic
Optic CharacterSR (Singly Refractive)
Dispersion0.007
Fluorescence LWStrong blue
Fluorescence SWVariable
Chelsea FilterInert
PleochroismNone
ColorsPurple, Blue Violet, Green, Yellow Orange, Colorless, Red Pink, Color Change
SpeciesFluorite
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 1.619–1.627; 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)
Price Context
Natural — low ($/ct)$2
Natural — high ($/ct)$20
NotePer carat; collector gem; too soft (4 Mohs) for most jewelry; color range is wide
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying a fluorite? GemID walks through these tests in order — RI, SG, fluorescence, and more.
Try GemID Free →Studying for the GIA, FGA, or FEEG practical? Fluorite is one of the 130 species in GemID’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
Practice exams →