---
title: "Moonstone: meaning in gemology"
description: "Moonstone is a feldspar gem: orthoclase with thin layers of albite inside. Light scattered between the layers gives a floating glow called adularescence."
url: https://digitalgemology.com/learn/glossary/moonstone
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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

# Moonstone

Also called rainbow moonstone

Moonstone is a feldspar gem: orthoclase with thin layers of albite inside. Light scattered between the layers gives a floating glow called adularescence.

## Properties

**Gemological properties of moonstone**

| Refractive index | 1.518 to 1.526 |
| --- | --- |
| Birefringence | 0.005 to 0.008 |
| Optic character | Doubly refractive (biaxial) |
| Dispersion | 0.012 |
| Specific gravity | 2.58 |
| Hardness (Mohs) | 6.0 to 6.5 |
| Crystal system | Monoclinic |
| Pleochroism | None |
| Absorption spectrum | Not diagnostic |

Published values. They change a little from stone to stone. Our tools do not model moonstone yet. Sources: [GIA](https://www.gia.edu/moonstone) · [Gemdat](https://www.gemdat.org/gem-3026.html) · [International Gem Society](https://www.gemsociety.org/article/moonstone-jewelry-gem-information/)

## In more detail

A blue sheen on a colorless background is a prized combination. Rainbow moonstone is not orthoclase: it is a variety of labradorite, another feldspar. Moonstone has poor toughness and two cleavage directions, so a hard blow can break it. Clean it only with warm, soapy water.

## Related terms

- [Cleavage](https://digitalgemology.com/learn/glossary/cleavage): Cleavage is a mineral's tendency to split along flat planes in its crystal structure. A hard knock in a cleavage direction can split a stone.
- [Toughness](https://digitalgemology.com/learn/glossary/toughness): Toughness is a gem's resistance to chipping and breaking. It differs from hardness, which is resistance to scratching.
- [Cabochon](https://digitalgemology.com/learn/glossary/cabochon): A cabochon is a gem polished to a smooth, convex dome, with no facets. It is one of the oldest and simplest cuts.
- [Chatoyancy](https://digitalgemology.com/learn/glossary/chatoyancy): Chatoyancy is a single band of light that glides across a gem, like the slit eye of a cat. Light reflects from many aligned, needle-like inclusions.

[All 369 terms](https://digitalgemology.com/learn/glossary)