Lapis Lazuli
Last updated: April 2026
A deep-blue metamorphic rock used as a semi-precious stone that is prized since antiquity.
Lapis Lazuli has a specific gravity of 2.75 and a refractive index of 1.500–1.670, with a Mohs hardness of 5.0–6.0. It is aggregate.
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
- Intense blue color
- Presence of golden pyrite flecks
- Aggregate rock, not a single mineral
Natural vs. Synthetic
Synthetic lapis lazuli is commercially available (Gilson synthetic (Bourgogne Lapis)). Distinguishing natural from synthetic typically requires microscopic examination of internal features.
- Visual / magnification: Irregular, varied blue saturation with white calcite patches and randomly distributed brass-yellow metallic pyrite flecks of varying size. Granular, slightly uneven surface texture. Synthetic: Gilson: too-uniform intense blue, no natural color variation, pyrite absent or too evenly distributed as fine brassy dust, calcite absent or as uniform specks, 'waxy' or 'sugary' even texture under magnification.
- Acetone test: No reaction — cotton swab stays clean, surface unchanged. Synthetic: Gilson synthetic: slight blue color transfer to swab, surface may become slightly sticky or dull.
- Glass imitation: Natural lapis has sub-vitreous luster, granular texture, pyrite and calcite. Synthetic: Glass: higher vitreous luster, perfectly smooth surface, no texture, gas bubbles under magnification, conchoidal fracture on chip, cold to touch.
Loupewise Pro includes a two-phase natural vs. synthetic testing protocol for Lapis Lazuli.
Treatments
- Dyed (to intensify or fake quality)
- Wax or oil impregnation
- Simulated (dyed howlite, sodalite, synthetic)
Measurement Guides
Identifying a lapis lazuli? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Lapis Lazuli 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 →