---
title: "Silk: meaning in gemology"
description: "Silk is a mass of fine, crossing needle inclusions, usually rutile, in ruby and sapphire."
url: https://digitalgemology.com/learn/glossary/silk
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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

# Silk

Also called rutile silk

Silk is a mass of fine, crossing needle inclusions, usually rutile, in ruby and sapphire.

## In more detail

A little silk scatters light and spreads color over dark areas, which can soften and even out the color. Too much silk lowers transparency and value. Intact silk shows that a stone was not heated to very high temperatures, but not that it was never heated.

## On a grading report

Not listed as a grade. Its state helps a lab decide between 'no indications of heating' and 'indications of heating'.

## Related terms

- [Needle](https://digitalgemology.com/learn/glossary/needle): A needle is a thin, elongated crystal inclusion that looks like a tiny rod at 10x.
- [Asterism](https://digitalgemology.com/learn/glossary/asterism): Asterism is a star of light that glides across the dome of a gem. Light reflects from fine needles, often rutile, that lie in two or three directions.
- [No indications of heating](https://digitalgemology.com/learn/glossary/no-indications-of-heating): 'No indications of heating' (NH) is the standard lab wording for a corundum that shows no signs of heat treatment.
- [Heat treatment](https://digitalgemology.com/learn/glossary/heat-treatment): Heat treatment is controlled heating of a gem to change its color or clarity.
- [Ruby](https://digitalgemology.com/learn/glossary/ruby): Ruby is the red variety of the mineral corundum. Chromium causes its red color.

## Learn more

- [Emerald Square Cut Ruby: a step-cut square that holds its light when tilted](https://digitalgemology.com/gemstones/ruby/emerald-square)

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