The Complete Gem Professional Reference: Key Facts at a Glance

This reference guide consolidates the most essential technical data for jewelry and gem professionals—hardness, refractive indices, specific gravities, common treatments, and care guidance for all major gem species. It is designed as a quick-reference companion to the complete Jewelswell Pillar 1 content library, enabling fast recall of key facts when working with clients or evaluating stones.

Big Four Precious Gems

Diamond — Hardness: 10 | RI: 2.417 | SG: 3.52 | Treatments: Fracture filling, HPHT, coating | Care: Avoid chlorine; ultrasonic safe (untreated)

Ruby (Corundum) — Hardness: 9 | RI: 1.762–1.778 | SG: 4.00 | Treatments: Heat (universal), fracture filling, glass filling | Care: Warm soapy water; ultrasonic safe (untreated/heat only)

Sapphire (Corundum) — Hardness: 9 | RI: 1.762–1.778 | SG: 4.00 | Treatments: Heat (common), beryllium diffusion | Care: Same as ruby

Emerald (Beryl) — Hardness: 7.5–8 | RI: 1.565–1.599 | SG: 2.72 | Treatments: Oil/resin filling (universal) | Care: Warm water only; no ultrasonic; no steam

Major Colored Gems

Alexandrite (Chrysoberyl) — Hardness: 8.5 | RI: 1.746–1.755 | SG: 3.73 | Treatments: None standard | Care: Excellent durability; ultrasonic safe

Tanzanite (Zoisite) — Hardness: 6.5 | RI: 1.691–1.700 | SG: 3.35 | Treatments: Heat (universal) | Care: No ultrasonic; no steam; protective settings recommended

Aquamarine (Beryl) — Hardness: 7.5–8 | RI: 1.567–1.590 | SG: 2.72 | Treatments: Heat (common to remove green) | Care: Good durability; ultrasonic generally safe

Spinel — Hardness: 8 | RI: 1.712–1.730 | SG: 3.60 | Treatments: Rarely treated | Care: Excellent durability; ultrasonic safe

Tourmaline — Hardness: 7–7.5 | RI: 1.624–1.644 | SG: 3.06 | Treatments: Heat, irradiation | Care: Good durability; gentle cleaning preferred

Garnet — Hardness: 6.5–7.5 | RI: 1.714–1.895 (varies by variety) | SG: 3.49–4.16 | Treatments: Rarely treated | Care: Good to excellent; most varieties ultrasonic safe

Opal — Hardness: 5.5–6.5 | RI: 1.37–1.52 | SG: 2.15 | Treatments: Impregnation, smoke treatment | Care: Avoid heat, chemicals, dehydration; no ultrasonic

Pearl — Hardness: 2.5–4.5 | RI: 1.52–1.66 | SG: 2.71 | Treatments: Bleaching, dyeing, luster enhancement | Care: Wipe after wearing; last on, first off; no chemicals

Peridot — Hardness: 6.5–7 | RI: 1.654–1.690 | SG: 3.34 | Treatments: Rarely treated | Care: Avoid acids; gentle cleaning; no ultrasonic

Amethyst/Citrine (Quartz) — Hardness: 7 | RI: 1.544–1.553 | SG: 2.65 | Treatments: Heat (amethyst to citrine) | Care: Good durability; ultrasonic generally safe

Mohs Hardness Quick Reference

10 — Diamond

9 — Corundum (ruby, sapphire)

8–8.5 — Chrysoberyl (alexandrite), spinel, topaz

7.5–8 — Beryl (emerald, aquamarine, morganite)

7–7.5 — Quartz, tourmaline, garnet (range)

6.5–7 — Tanzanite, peridot, jade (jadeite)

6–6.5 — Labradorite, moonstone, opal

5.5–6 — Lapis lazuli, turquoise

2.5–4.5 — Pearl, coral, amber (organic gems)

Treatment Disclosure Quick Reference

Always disclose: Glass filling in ruby, significant oil in emerald, beryllium diffusion in sapphire, irradiation in colored diamonds

Disclose as standard practice: Heat treatment in corundum, oil in emerald, wax/resin in turquoise

No treatment needed: Untreated status is a value premium—always certify and document

Lab reports: GIA, Gübelin, SSEF, GRS — accepted at major auction houses; required for investment-grade stones

Universal Care Rules for All Gems

Avoid exposure to household chemicals, perfumes, hairspray, and cleaning products

Store gems individually to prevent contact scratching

Clean with warm water and mild soap unless otherwise specified

Never use ultrasonic or steam for soft, fragile, or treated gems

Remove jewelry before exercise, swimming, or heavy work

Have prongs and settings checked by a professional annually