---
title: "Dichroscope: meaning in gemology"
description: "A dichroscope is a gem-testing instrument that shows a stone's two pleochroic colors side by side. In the calcite type, a calcite rhomb splits the light…"
url: https://digitalgemology.com/learn/glossary/dichroscope
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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

# Dichroscope

Also called calcite dichroscope, London dichroscope

A dichroscope is a gem-testing instrument that shows a stone's two pleochroic colors side by side. In the calcite type, a calcite rhomb splits the light into two images of a small window.

## In more detail

The two images carry light that vibrates at right angles. Two different colors show that the stone is doubly refractive and pleochroic. Matching colors prove nothing: a singly refractive stone, a colorless one, or a view down the optic axis all match. A London dichroscope uses two polarizing filters instead of calcite.

## How we measure it

Our Dichroscope computes the window colors from measured polarized absorption spectra, through 5 mm in daylight (D65). It is a teaching model, not a test of a real stone.

## Related terms

- [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.
- [Ordinary ray](https://digitalgemology.com/learn/glossary/ordinary-ray): The ordinary ray (o-ray) is the ray in a uniaxial stone that vibrates across the optic axis. It has the same refractive index, ω or nₒ, in every direction.
- [Extraordinary ray](https://digitalgemology.com/learn/glossary/extraordinary-ray): In a uniaxial stone, the extraordinary ray (e-ray) vibrates in the plane of the optic axis and the light path. Its refractive index changes with direction, from ω along the axis to ε across it.
- [CIEDE2000 color difference](https://digitalgemology.com/learn/glossary/ciede2000): CIEDE2000 (ΔE00) is a standard formula for how different two colors look to a human observer. A larger number means a larger visible difference.

## Learn more

- [Dichroscope](https://digitalgemology.com/tools/dichroscope)
- [Dichroscope](https://digitalgemology.com/about/how-we-measure/dichroscope)

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