Prehnite
Last updated: April 2026
Pale apple-green prehnite is common in estate jewelry as cabochons and beads, often confused with jade or green glass. Lower RI (1.611–1.665) and SG separate it from jadeite; fibrous internal texture is often visible under loupe. Frequently intergrown with epidote (yellowish-green crystals).
Prehnite has a specific gravity of 2.88 and a refractive index of 1.611–1.665, with a Mohs hardness of 6.0–6.5. It is biaxial +.
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
- Pale apple-green to yellow-green color typical
- RI 1.611–1.665 — lower than jadeite (1.654–1.688)
- SG 2.82–2.94 — much lower than jadeite (3.25–3.40)
- Often shows fibrous internal texture under 10x loupe
- Frequently associated with epidote inclusions (yellowish-green crystals)
Common Simulants
- Jadeite jade: Jadeite: RI 1.666; SG 3.34; higher luster; more uniform color; harder (6.5–7 Mohs).
- Nephrite jade: Nephrite: aggregate fibrous; SG 2.90–3.03; tougher; RI 1.600–1.627.
Measurement Guides
Identifying a prehnite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Prehnite 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 →