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Amazonite

Last updated: April 2026

Blue-green microcline feldspar colored by lead and water; frequently sold as a turquoise alternative. Under magnification, whitish cross-hatch or grid twinning (perthitic albite intergrowth) is visible in most specimens and is a key field indicator. Distinguished from turquoise by lower RI and SG; from chrysoprase by higher RI; from jade by lower RI/SG and cleavage. No pleochroic colour pair is recorded: O’Donoghue (Gems, 6th ed., 2006, via gemdat) gives microcline’s pleochroism as weak and names no colours, and the same reference has the material translucent to opaque and only rarely transparent — pleochroism is differential absorption of transmitted light, so there is usually nothing to read.

Amazonite has a specific gravity of 2.56 and a refractive index of 1.514–1.530, with a Mohs hardness of 6.0–6.5. It is biaxial −.

Physical & Optical Properties

RI Range1.514–1.530
SG Range2.54–2.58
SG Typical2.56
Hardness (Mohs)6–6.5
Crystal SystemTriclinic
Optic CharacterDR Biaxial (−)
Birefringence0.008
Dispersion0.012
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismWeak
ColorsGreen, Blue Violet
SpeciesFeldspar
VarietyMicrocline
GreenBlue 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

Amazonite reads 1.518 – 1.526 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 0.008 apart — so close that at this size theyread as one thick line. On the instrument they separate onlywith a steady head and a sharp edge. 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

Amazonite Blinks 4× per turn (DR) 0° 45° 90° 135° ROTATION BETWEEN CROSSED POLARS Amazonite 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

Amazonite SG 2.54–2.58 WHERE IT SITS, AND WHAT ELSE IS THERE 1.0 2.0 3.0 4.0 5.0 SPECIFIC GRAVITY 16 other species in the table overlap this range, so a reading here narrows the field to 17 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

Amazonite weak — colours not recorded COLOURS NOT IN OUR SOURCE Amazonite is recorded as showing weak pleochroism, but our source does not name the two colours, so this figure does not paint them. The windows will differ; which hues they take is not something we hold. 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.

LabradoriteMoonstoneRainbow MoonstoneSunstone

Key Differentiators

Common Simulants

Commonly Confused With

Commonly confused with: Turquoise, Jadeite, Nephrite.

Treatments

Measurement Guides

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

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

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Studying for the GIA, FGA, or FEEG practical? Amazonite is one of the 132 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.

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