36Learning guidesFamilies, glossary & next chaptersNavigate the mineral families and the language of colour, light and provenance.
72 gem-material topics, twenty jewellery-house essays and eight educational guides in the expanded library. Curated coverage, not every gem material or every mineral.
Corundum
Red corundum is ruby; other gem colours belong under sapphire.
Members in this edition: ruby, sapphire.
Evidence: GIA: ruby, GIA: ruby description, GIA: sapphire, GIA: sapphire description
Beryl
Colour varieties share a mineral framework; inclusions and treatments can make practical durability very different.
Members in this edition: emerald, aquamarine, morganite.
Evidence: GIA: aquamarine, GIA: aquamarine description, GIA: emerald, GIA: emerald description, GIA: morganite, GIA: morganite description
Quartz
This edition includes crystalline quartz gems and selected chalcedony materials. Their separate profiles explain the distinctions in more detail.
Members in this edition: amethyst, citrine, ametrine, rose quartz, rock crystal, smoky quartz, agate, carnelian, chrysoprase, onyx and jasper.
Evidence: GIA: amethyst, GIA: amethyst description, GIA: ametrine, GIA: ametrine description, GIA: citrine, GIA: citrine description, GIA: rose quartz, GIA: rose quartz description
Feldspar
Both gem names can encompass more than one feldspar material. Identify the actual material where relevant.
Members in this edition: moonstone, sunstone.
Evidence: GIA: moonstone, GIA: moonstone description, GIA: sunstone, GIA: sunstone description
Garnet group
Pyrope, almandine, spessartine, grossular and andradite are major gem members. Tsavorite and demantoid are varieties, not separate species.
Members in this edition: garnet.
Evidence: GIA: garnet, GIA: garnet description
Tourmaline group
Species and colourful trade names are different layers of classification.
Members in this edition: tourmaline.
Evidence: GIA: tourmaline, GIA: tourmaline description
Organic and biogenic gems
Includes living-system origins. Cultured pearl is a distinct production category from laboratory-grown mineral gems.
Members in this edition: amber, pearl.
Evidence: GIA: amber, GIA: amber description, GIA: pearl, GIA: pearl description
Adularescence
A floating or billowing sheen associated with fine internal structures in feldspar.
Evidence for this definition: GIA: Moonstone description
Asterism
A star-like reflection produced by appropriately oriented inclusions and revealed by suitable cutting.
Evidence for this definition: GIA: Sapphire description · GIA: Ruby description
Aventurescence
Glitter from reflective inclusions within a material.
Evidence for this definition: GIA: Sunstone description
Cabochon
A shaped, polished gem with a curved surface rather than a crown of facets.
Evidence for this definition: GIA: Moonstone description
Chatoyancy
A band of reflected light that moves like a cat’s eye, usually shown in a cabochon.
Evidence for this definition: GIA: Cat’s-Eye Chrysoberyl
Cleavage
A tendency to split along particular crystallographic directions.
Evidence for this definition: GIA: Topaz description
Colour Change
A change in apparent colour between different kinds of illumination.
Evidence for this definition: GIA: Alexandrite description
Dispersion
Separation of light into spectral colours, seen as coloured flashes in some cut gems.
Evidence for this definition: GIA: Diamond description · GIA: Zircon description
Fluorescence
Visible emission produced during suitable excitation; it is distinct from ordinary body colour.
Evidence for this definition: GIA: Diamond fluorescence
Inclusion
An internal feature such as a crystal, fluid pocket or growth structure.
Evidence for this definition: GIA: Emerald quality factors
Matrix
Host material retained with or surrounding the gem.
Evidence for this definition: GIA: Emerald geology
Pleochroism
Different colours seen along different directions through certain crystals.
Evidence for this definition: GIA: Iolite description
Play Of Colour
Shifting spectral colours in precious opal, produced by diffraction.
Evidence for this definition: GIA: Opal description
Provenance
An object’s documented ownership or custody history; this is not identical to geological origin.
Evidence for this definition: GIA: Geographic origin determination of emerald
Toughness
Resistance to breaking or chipping, distinct from scratch hardness.
Evidence for this definition: GIA: Topaz care and cleaning
Current coverage and further themes
Available in this edition: agate, carnelian, chrysoprase, onyx and jasper.
Available in this edition: rock crystal and smoky quartz.
Available in this edition: cat’s-eye chrysoberyl, alongside the existing alexandrite study.
Additional feldspars beyond the present selection include labradorite and amazonite.
Further collector-gem topics include apatite, fluorite, sphene, diopside, kyanite, andalusite and sphalerite.
This is a defined learning collection, not an exhaustive encyclopedia. Further ornamental and organic materials need their own evidence and legal or conservation context.
Evidence:
Sources & reading
- GIA: alexandriteGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: alexandrite descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: amberGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: amber descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: amethystGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: amethyst descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: ametrineGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: ametrine descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: aquamarineGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: aquamarine descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: citrineGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: citrine descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: diamondGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: diamond descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: emeraldGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: emerald descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: garnetGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: garnet descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: ioliteGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: iolite descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: jadeGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: jade descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: kunziteGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: kunzite descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: lapis lazuliGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: moonstoneGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: moonstone descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: morganiteGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: morganite descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: opalGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: opal descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: pearlGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: pearl descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: peridotGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: peridot descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: rose quartzGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: rose quartz descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: rubyGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: ruby descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: sapphireGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: sapphire descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: spinelGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: spinel descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: sunstoneGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: sunstone descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: tanzaniteGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: tanzanite descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: topazGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: topaz descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: tourmalineGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: tourmaline descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: turquoiseGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: turquoise descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: zirconGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.
- GIA: zircon descriptionGIA · 2026-10-03
Selected material reference for the terminology used throughout this collection.