About gemmology.dev

gemmology.dev is an open, FGA-aligned reference and study toolkit for coloured gemstones. Everything here – the 159-mineral family reference, 216 crystal expressions, the Crystal Description Language (CDL), the calculators, and the quiz – is free and open-source.

Who maintains this

gemmology.dev is maintained by the gemmology-dev open-source project. Contributions, corrections, and source citations from the gemmological community are welcomed via GitHub issues and pull requests.

Editorial standards

  • Curriculum alignment. Reference content follows the published Fellowship of the Gemmological Association (FGA) Diploma syllabus structure for crystal systems, optical and physical properties, equipment, and identification.
  • Numerical data. Refractive index, specific gravity, birefringence, and dispersion ranges are sourced from peer-reviewed gemmological references and verified across multiple sources before inclusion.
  • Crystal morphology. Crystal structures are described using CDL (a domain-specific language documented at /docs/cdl), rendered from formal Miller indices and point-group symmetry rather than artistic impressions.
  • Synthetics & simulants. Lab-grown materials are labelled by growth method (CVD, HPHT, flux, hydrothermal, Verneuil, Czochralski) and linked to their natural counterparts where one exists.
  • Reviewed dates. Each learn article shows when it was last reviewed. Out-of-date pages are flagged for refresh.

Sources & further reading

  • Gem-A: Gem Testing (Anderson / Webster), Gems & Gemmology (FGA notes)
  • GIA: Gems & Gemology journal, GIA Reference Guides
  • Mindat.org for locality and chemistry cross-checks
  • Schumann, Walter. Gemstones of the World
  • Read, Peter. Gemmology

What is not here

  • Commercial appraisals or price guidance
  • Real-time market or auction data
  • Authentication or certification: gemmology.dev is a study tool, not a lab

Reporting an error

Spotted incorrect data, a missing reference, or a broken figure? Open an issue at github.com/gemmology-dev/gemmology.dev/issues. Corrections are usually shipped within a week.

Licence

Code is MIT-licensed. Educational content (the learn articles and curriculum data in gemmology-knowledge) is published under CC BY-SA 4.0.