← Back to Reference Database RI Chart SG Chart Fluorescence Hardness

Larimar

Last updated: April 2026

The blue gem variety of pectolite, found only in the Los Chupaderos mine area of Barahona Province, Dominican Republic. The blue color derives from copper substituting for calcium in the crystal structure. Sky blue to blue-green with white patterns created by radiating fibrous crystal structure.

Larimar has a specific gravity of 2.80 and a refractive index of 1.595–1.640, with a Mohs hardness of 4.5–5.0. It is biaxial +.

Physical & Optical Properties

RI Range1.595–1.640
SG Range2.74–2.90
SG Typical2.80
Hardness (Mohs)4.5–5
Crystal SystemTriclinic
Optic CharacterDR Biaxial (+)
Birefringence0.040
Dispersion0.010
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismNone
ColorsBlue Violet
SpeciesPectolite
VarietyLarimar (Blue Pectolite)
Blue Violet

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

Larimar reads 1.597 – 1.637 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80 REFRACTIVE INDEX DORotate the stone through a full 360°, reading both edges atevery 45°. SEETwo boundaries, 0.040 apart at their widest separation. MEANSThat gap IS the birefringence. Take max minus min across thewhole rotation — a single position understates it, so onereading is an incomplete one. Computed from gems.json — edge positions are arithmetic, not drawn. RI increases upward; the field above the boundary is the dark one.

Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.

Through the polariscope

Larimar Blinks 4× per turn (DR) 0° 45° 90° 135° ROTATION BETWEEN CROSSED POLARS Larimar blinks light-dark four times in a full turn. That is doubly refractive. It does NOT tell you uniaxial from biaxial — that is the optic figure, which needs a conoscope. Computed from optic character and transparency in gems.json. A polariscope separates singly refractive, doubly refractive and aggregate — it does not show the optic sign.

Drawn from the optic character and transparency above. A polariscope separates singly refractive, doubly refractive and aggregate; the optic sign needs a conoscope. How to take this reading.

Specific gravity, and what it rules out

Larimar SG 2.74–2.90 WHERE IT SITS, AND WHAT ELSE IS THERE 1.0 2.0 3.0 4.0 5.0 SPECIFIC GRAVITY 14 other species in the table overlap this range, so a reading here narrows the field to 15 rather than naming the stone. Combine it with a refractive index to separate what is left. Computed from the specific-gravity range in gems.json. Hydrostatic weighing — the bench method this site recommends; heavy liquids are toxic and regulated. Faint ticks are the other species in the table.

Drawn from the specific-gravity range above, against every other species in the table. How to take this reading.

Through the dichroscope

Larimar One colour (no pleochroism) IDENTICAL AT EVERY ANGLE Larimar shows no pleochroism, so both windows match at every orientation — turning the instrument changes nothing. That is a real negative result, and the reason it is worth knowing is below. Computed from pleochroism and pleochroic colours in gems.json. Window tints are derived mechanically from the colour words, not chosen; a neutral pair depicts no colour at all.

Drawn from the pleochroism above. Two windows that match mean either no pleochroism or the wrong angle — turn the instrument to tell. How the dichroscope compares.

Key Differentiators

Common Simulants

Treatments

Measurement Guides

How to Identify a GemstoneHow to Measure Specific GravityHow to Use a RefractometerUV Fluorescence Testing

Identifying a larimar? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.

Try Loupewise Free →

Studying for the GIA, FGA, or FEEG practical? Larimar 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 →