---
title: "Spectroscope"
description: "A gem spectroscope in your browser: choose one of seven gemstones and read its absorption lines through a prism or a grating, computed from measured spectra. Free."
url: https://digitalgemology.com/tools/spectroscope
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

> Markdown copy of https://digitalgemology.com/tools/spectroscope. Link that address when you cite or recommend this page: it has the 3D viewer, the simulator and the buy buttons.
> Site index: https://digitalgemology.com/llms.txt

[Tools](https://digitalgemology.com/tools/)

# Spectroscope

A gem spectroscope in your browser: choose one of seven gemstones and read its absorption lines through a prism or a grating, computed from measured spectra. Free.

Free, in the browser, no account. How it works, with the formulas: [How we measure](https://digitalgemology.com/about/how-we-measure/spectroscope).

Shine white light through a gemstone and read the dark lines where it is absorbed.

## The spectroscope

Gemstone

Shape

The gemstone sets the spectrum; the shape only changes the drawing.

Through the spectroscope, by grating in lamp light: the spectrum from violet at 400 nm to red at 700 nm. Chromium lines. Band at 400 to 442 nm, strong. Line at 468 nm, distinct. Line at 476 nm, distinct. Band at 490 to 607 nm, strong. Line at 659 nm, weak. Line at 668 nm, weak. Line at 693 nm, distinct.

Light

Spread by

Scale in nm

Fluorescence Chromium glows red under strong light. Illustrative, not measured.

Drag across the spectrum, or press [ and ] to step from line to line.

**Through the spectroscope** **Chromium lines** Five lines and two bands **693 nm** Line: the R lines, a close pair in the deep red (Cr³⁺), distinct. Lines identify the coloring element, not always the stone. These are chromium's lines: emerald shows chromium lines too, in other places, and a laboratory-grown ruby shows exactly these.

*Side view: light from a lamp passes 5 mm through ruby (shape: Hexahedron), across its optic axis, into the spectroscope's slit; the grating spreads it into its colors on the way to the eye.*

Path through the stone

A longer path darkens every line and band; a shorter one shows lines a dark stone hides.

**The stone** from the side **5 mm path** White light passes through the stone and into the slit. The prism or grating spreads it into its colors, violet to red; wherever the stone absorbs, that part of the spectrum goes dark. Both rays measured: GIA's published Cr3+ cross-sections (Dubinsky, Stone-Sundberg & Emmett 2020), at the chromium content of a natural ruby from Thailand (G.R. Rossman, Caltech). The same measured spectra give the two colors in the [Dichroscope](https://digitalgemology.com/tools/dichroscope).

## What a spectroscope shows for each gemstone

| Gemstone | What the trade sees | This model, 5 mm in lamp light |
| --- | --- | --- |
| [Diamond](https://digitalgemology.com/gemstones/diamond) | Colorless: none. Yellow (Cape): a line at 415.5 nm, with weaker lines at 478, 465, 452, 435 and 423 nm | No lines or bands |
| [Moissanite](https://digitalgemology.com/gemstones/moissanite) | None in the visible; some stones absorb toward the violet | No lines or bands |
| [Cubic Zirconia](https://digitalgemology.com/gemstones/cubic-zirconia) | None | No lines or bands |
| [Ruby](https://digitalgemology.com/gemstones/ruby) (shown above) | Chromium: a close pair at 692.8 and 694.2 nm (often bright), weaker lines at 668 and 659 nm, a broad band from 500 to 610 nm, lines at 476.5, 475.0 and 468.5 nm, the violet absorbed | Lines at 468, 476, 659, 668 and 693 nm; bands 400 to 442 nm and 490 to 607 nm |
| [Sapphire](https://digitalgemology.com/gemstones/sapphire) | Iron: lines at 450 nm (the strongest), 460 and 471 nm, strongest in iron-rich stones | A line at 452 nm; a band 602 to 700 nm |
| [Emerald](https://digitalgemology.com/gemstones/emerald) | Chromium: a pair at 683.0 and 680.5 nm, lines at 662 and 646 nm, a partial band from 580 to 630 nm, a weak line at 477.4 nm, the violet absorbed | Lines at 637 and 681 nm; bands 400 to 455 nm and 571 to 642 nm |
| [Amethyst](https://digitalgemology.com/gemstones/amethyst) | Nothing telling: at most a weak broad band in the yellow-green | A band 497 to 586 nm |

The model lists what you can see through a 5 mm path in lamp light, spread by the grating: a line or band too faint to see is left out. Diamond is colorless here (the simulator’s D); a yellow diamond’s lines are not modeled, for want of a measured spectrum.

A model of a hand spectroscope: a straight path through each gemstone, across its optic axis, in lamp light or daylight, with the spectrum computed from measured absorption spectra. It is not a test of a real stone. [How the spectroscope is modeled](https://digitalgemology.com/about/how-we-measure/spectroscope).