---
title: "Singly refractive: meaning in gemology"
description: "A singly refractive stone has one refractive index in every direction, so light stays one ray inside it. Diamond and cubic zirconia are singly refractive."
url: https://digitalgemology.com/learn/glossary/singly-refractive
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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

# Singly refractive

Also called isotropic, SR

A singly refractive stone has one refractive index in every direction, so light stays one ray inside it. Diamond and cubic zirconia are singly refractive.

## In more detail

A singly refractive stone stays dark between crossed polarizers at every turn. A doubly refractive stone also stays dark when you look down its optic axis. So dark alone does not prove single refraction. Strain can make a singly refractive stone show patchy light.

## How we measure it

The Polariscope shows diamond and cubic zirconia staying dark at every turn and tilt. Our build checks that no light passes them.

## Related terms

- [Doubly refractive](https://digitalgemology.com/learn/glossary/doubly-refractive): A doubly refractive stone splits light into two rays that vibrate at right angles and travel at different speeds. Each ray has its own refractive index.
- [Polariscope](https://digitalgemology.com/learn/glossary/polariscope): A polariscope is a gem-testing instrument with a stone between two polarizing filters. With the filters crossed, it shows whether a stone is singly refractive, doubly refractive, strained or an aggregate.
- [Strain](https://digitalgemology.com/learn/glossary/strain): Strain is internal stress that makes a singly refractive stone weakly doubly refractive in patches. Between crossed polarizers it shows as patchy light that never goes dark all at once.
- [Crystal system](https://digitalgemology.com/learn/glossary/crystal-system): A crystal system groups crystals by the symmetry of their atomic structure. Gemologists use seven: cubic, tetragonal, hexagonal, trigonal, orthorhombic, monoclinic and triclinic.

## Learn more

- [Polariscope](https://digitalgemology.com/about/how-we-measure/polariscope)
- [Polariscope](https://digitalgemology.com/tools/polariscope)
- [Diamond testers and moissanite: what the instruments say](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite)

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