---
title: "Biaxial: meaning in gemology"
description: "A biaxial stone is a doubly refractive stone with two optic axes. It can show three colors in a dichroscope, and its interference figure differs from a…"
url: https://digitalgemology.com/learn/glossary/biaxial
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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[Glossary](https://digitalgemology.com/learn/glossary) · Optics

# Biaxial

A biaxial stone is a doubly refractive stone with two optic axes. It can show three colors in a dichroscope, and its interference figure differs from a uniaxial one.

## In more detail

Tanzanite and iolite are biaxial. On a refractometer, both shadow edges of a biaxial stone can move as the stone turns.

## How we measure it

None of the seven gemstones in our tools is biaxial, so the tools do not model biaxial stones.

## Related terms

- [Uniaxial](https://digitalgemology.com/learn/glossary/uniaxial): A uniaxial stone is a doubly refractive stone with one optic axis. Moissanite, emerald, ruby, sapphire and amethyst are uniaxial.
- [Optic axis](https://digitalgemology.com/learn/glossary/optic-axis): An optic axis is a direction in a doubly refractive crystal along which light does not split into two rays. Seen along it, the stone behaves as if it were singly refractive.
- [Pleochroism](https://digitalgemology.com/learn/glossary/pleochroism): Pleochroism is the property of a colored doubly refractive stone to show different colors in different directions. It happens because the stone absorbs its rays differently.
- [Interference figure](https://digitalgemology.com/learn/glossary/interference-figure): An interference figure is the pattern of colors and dark bands that a doubly refractive stone shows through a conoscope. Each point of the figure is one direction through the stone.

## Learn more

- [Polariscope](https://digitalgemology.com/about/how-we-measure/polariscope)
- [Dichroscope](https://digitalgemology.com/about/how-we-measure/dichroscope)
- [Refractometer](https://digitalgemology.com/about/how-we-measure/refractometer)

[All 328 terms](https://digitalgemology.com/learn/glossary)