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Pietersite

Last updated: April 2026

Trade name for a brecciated aggregate of hawk's eye (blue crocidolite-replaced quartz) and tiger's eye (iron-oxide-stained quartz), with angular fragments re-cemented by secondary silica. Discovered in Namibia in 1962. The mixture of blue, gold, and red in a brecciated pattern is visually distinctive.

Pietersite has a specific gravity of 2.61 and a refractive index of 1.534–1.540, with a Mohs hardness of 6.5–7.0. It is aggregate.

Physical & Optical Properties

RI Range1.534–1.540
SG Range2.58–2.64
SG Typical2.61
Hardness (Mohs)6.5–7
Crystal SystemAggregate
Optic CharacterAggregate
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismNone
ColorsMulti, Blue Violet, Brown, Yellow Orange
SpeciesPietersite (brecciated hawk's eye and tiger's eye — crocidolite/quartz aggregate)
MultiBlue VioletBrownYellow Orange

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

Pietersite reads 1.537 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°, watching the boundary. SEEOne boundary, at 1.537, and it does not move as you rotate. MEANSThis is an aggregate — a mass of microscopic crystals — andon this instrument it looks exactly like a singly refractivestone. The refractometer cannot tell the two apart. Thepolariscope can: an aggregate stays light through a fullrotation, where a singly refractive stone stays dark. 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

Pietersite No reading ANY POSITION — THE STONE BLOCKS THE LIGHT BETWEEN CROSSED POLARS Pietersite is opaque, so no light reaches the analyser. The field stays dark in every position — not because the stone is singly refractive, but because the test cannot be run on it at all. SR, DR and aggregate cannot be separated this way. 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

Pietersite SG 2.58–2.64 WHERE IT SITS, AND WHAT ELSE IS THERE 1.0 2.0 3.0 4.0 5.0 SPECIFIC GRAVITY 30 other species in the table overlap this range, so a reading here narrows the field to 31 rather than naming the stone. This is the crowded part of the scale — the same careful measurement is worth far more higher up. 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

Pietersite No reading NO LIGHT THROUGH THE STONE Pietersite is opaque. A dichroscope reads light that has passed THROUGH the stone, so there is nothing to split and no reading to take — the same limit that rules out the polariscope. 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 pietersite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.

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Studying for the GIA, FGA, or FEEG practical? Pietersite 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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