A-Z of Gemstones

A complete guide to gemstones, including colour, lustre, hardness, toughness, cutting styles, discovery, and crystal system, from Alexandrite to Zircon...

Alexandrite and Other Chrysoberyls

• Hardness: 8.5

• Toughness: Excellent

• Lustre: Vitreous

• Colour: Green to red (alexandrite), yellow to green (chrysoberyl)

• Cutting Styles: Ovals, cushions, cat’s eye (chatoyancy)

• Discovered: 1830s (Russia)

• Crystal System: Orthorhombic

Amethyst

• Hardness: 7

• Toughness: Fair to good

• Lustre: Vitreous

• Colour: Light lilac to deep purple

• Cutting Styles: Rounds, ovals, antique step cuts

• Crystal System: Trigonal

Aquamarine

• Hardness: 7.5–8

• Toughness: Good

• Lustre: Vitreous

• Colour: Light to deep blue

• Cutting Styles: Emerald cuts, ovals, step cuts

• Crystal System: Hexagonal

Other Beryls (Morganite, Heliodor, Goshenite)

• Hardness: 7.5–8

• Toughness: Good

• Lustre: Vitreous

• Colour: Pink, yellow, colourless

• Cutting Styles: Mixed, step, brilliant

• Crystal System: Hexagonal

Chalcedony

• Hardness: 6.5–7

• Toughness: Excellent

• Lustre: Waxy to dull

• Colour: Pale blue, grey, lavender

• Cutting Styles: Cabochons, intaglios, cameos

• Crystal System: Trigonal (microcrystalline quartz)

Citrine

• Hardness: 7

• Toughness: Good

• Lustre: Vitreous

• Colour: Pale yellow to amber

• Cutting Styles: Step and brilliant cuts

• Crystal System: Trigonal

Emerald

• Hardness: 7.5–8

• Toughness: Poor to fair

• Lustre: Vitreous

• Colour: Deep green to bluish green

• Cutting Styles: Emerald cut, ovals

• Crystal System: Hexagonal

Feldspar Group (Moonstone, Labradorite, Sunstone)

• Hardness: 6–6.5

• Toughness: Poor to fair

• Lustre: Vitreous to pearly

• Colour: Various (blue, peach, green, iridescent)

• Cutting Styles: Cabochons, fancy shapes

• Crystal System: Monoclinic (orthoclase), Triclinic (plagioclase)

Garnet Group

• Hardness: 6.5–7.5

• Toughness: Good

• Lustre: Vitreous to resinous

• Colour: Red, green, orange, pink

• Cutting Styles: Antique rose cuts, rounds, ovals

• Crystal System: Isometric

Jade and Nephrite

• Hardness: 6–7

• Toughness: Excellent

• Lustre: Greasy to waxy

• Colour: Green, white, lavender

• Cutting Styles: Cabochons, carvings

• Crystal System:

  • Jadeite: Monoclinic

  • Nephrite: Monoclinic (amphibole group)

Kunzite

• Hardness: 6.5–7

• Toughness: Poor

• Lustre: Vitreous

• Colour: Pale pink to violet

• Cutting Styles: Emerald and step cuts

• Discovered: Early 20th century

• Crystal System: Monoclinic

Lapis Lazuli

• Hardness: 5–6

• Toughness: Fair

• Lustre: Waxy to dull

• Colour: Deep royal blue with pyrite inclusions

• Cutting Styles: Cabochons, plaques

• Crystal System: Not a single mineral – mainly Lazurite (isometric)

Opal

• Hardness: 5.5–6.5

• Toughness: Poor

• Lustre: Vitreous to pearly

• Colour: Milky white to black with play-of-colour

• Cutting Styles: Cabochons, freeforms

• Crystal System: Amorphous (not crystalline)

Organic and Biogenic Gem Materials

(Includes pearl, amber, coral, jet)

• Hardness: Varies (2.5–4.5)

• Toughness: Generally poor

• Lustre: Pearly, resinous, dull

• Colour: White, cream, black, red, golden, brown

• Cutting Styles: Beads, cabochons, carvings

• Crystal System: Organic – no defined crystal structure

Peridot

• Hardness: 6.5–7

• Toughness: Fair

• Lustre: Vitreous

• Colour: Olive to lime green

• Cutting Styles: Ovals, rounds, step cuts

• Crystal System: Orthorhombic

Quartz Group (including Rose Quartz, Smoky Quartz, Rock Crystal)

• Hardness: 7

• Toughness: Good

• Lustre: Vitreous

• Colour: Colourless, pink, brown, grey

• Cutting Styles: Brilliant, step cuts, cabochons

• Crystal System: Trigonal

Ruby

• Hardness: 9

• Toughness: Excellent

• Lustre: Vitreous

• Colour: Red to purplish red

• Cutting Styles: Cushion, oval, mixed cuts

• Crystal System: Trigonal

Sapphire

• Hardness: 9

• Toughness: Excellent

• Lustre: Vitreous

• Colour: Blue, yellow, green, pink, colourless

• Cutting Styles: Ovals, step cuts, cabochons (star sapphires)

• Crystal System: Trigonal

Spinel

• Hardness: 8

• Toughness: Good

• Lustre: Vitreous

• Colour: Red, pink, violet, blue

• Cutting Styles: Ovals, antique brilliant cuts

• Crystal System: Isometric

Tanzanite

• Hardness: 6–7

• Toughness: Poor to fair

• Lustre: Vitreous

• Colour: Blue to violet-blue

• Cutting Styles: Emerald and step cuts

• Discovered: 1967

• Crystal System: Orthorhombic

Topaz

• Hardness: 8

• Toughness: Poor (perfect cleavage)

• Lustre: Vitreous

• Colour: Blue, yellow, pink, golden, clear

• Cutting Styles: Ovals, pears, emerald cuts

• Crystal System: Orthorhombic

Tourmaline

• Hardness: 7–7.5

• Toughness: Good

• Lustre: Vitreous

• Colour: All colours, often bi-colour

• Cutting Styles: Fancy cuts, cabochons (cat’s eye)

• Crystal System: Trigonal

Turquoise

• Hardness: 5–6

• Toughness: Fair

• Lustre: Waxy to dull

• Colour: Sky blue to green

• Cutting Styles: Cabochons, beads

• Crystal System: Triclinic

Zircon

• Hardness: 6–7.5

• Toughness: Fair

• Lustre: Adamantine

• Colour: Blue, brown, yellow, red, green, clear

• Cutting Styles: Round brilliant, antique cushion

• Crystal System: Tetragonal