GEMSTONE FIELD GUIDE
Sapphire
Ruby and sapphire are varieties of one mineral species, not separate mineral species.
Actual 4.71 ct oval sapphire from Malawi, NMNH G11482. Photograph by Greg Polley. Reference specimen—not NumisTrends inventory.
One photograph only. The blue faceted gem is suitable for a photo-first sapphire reference, but not rotation or a 3D claim. Museum catalog facts belong to G11482, not other sapphire images or a generic sapphire profile.
Greg Polley, Smithsonian National Museum of Natural History, NMNH G11482. CC0. · Source ↗ · CC0-1.0 · resized for the webActual source photographs. Each caption identifies its specimen. Alternate photographs are not a 360° scan.
A verified 3D specimen capture is not available for this entry. No generated stand-in is used.
AT A GLANCE
Start with the evidence.
Assess the whole stone, not just its color or one exposed facet. Treatment and assembled construction can complicate apparently sapphire-like results.
- GIA — Synthetic sapphire and synthetic spinel doublets (Winter 2016) ↗
- GIA — Madagascar sapphire heat-treatment study (Summer 2019) ↗
- Refractive index (RI)
- 1.762–1.770
- Specific gravity (SG)
- 4.00 · typical
- Mohs hardness
- 9
typical interval
How to read this value
Published reference interval, not necessarily the two readings of every specimen and not an exhaustive identity boundary. Composition, orientation, wavelength, instrument and condition matter.
How to read this value
GIA's sapphire overview publishes 4.00 without numerical tolerance; no range has been invented here.
How to read this value
Scratch resistance, not toughness. This ordinal scale is not linear.
These are reference properties, not measurements of the pictured specimen. Reference images are educational—not NumisTrends sale inventory.
See the details and limitations ↓01 · IDENTIFY
Build a profile, not a guess.
Typical material-level reference; not a measurement, identification, origin, treatment determination, or grading result for any specimen.
Refractive index (RI)1.762–1.770
typical interval
Published reference interval, not necessarily the two readings of every specimen and not an exhaustive identity boundary. Composition, orientation, wavelength, instrument and condition matter.
Specific gravity (SG)4.00 · typical
GIA's sapphire overview publishes 4.00 without numerical tolerance; no range has been invented here.
Mohs hardness9
Scratch resistance, not toughness. This ordinal scale is not linear.
Birefringence0.008–0.010
Typical published birefringence range; do not calculate each specimen's birefringence by subtracting the population RI endpoints.
Optic characterUniaxial negative
CleavageNone
Inclusions, fractures and treatment-related weaknesses may still affect durability.
Open a property for its scope and source. RI and specific gravity have no units. Mohs describes scratch resistance—not resistance to breaking. Do not scratch a stone to test it.
What can look similar?
Synthetic spinel
Manufactured spinel can imitate sapphire colors.
How to investigate. Identify optical properties and inspect the entire stone; laboratory analysis can confirm ambiguous material.
It can also occur as one component of an assembled stone.
Laboratory-grown sapphire
Artificial growth can produce the same gem material.
How to investigate. Flame-fusion material can show curved growth banding; trained microscopy and appropriate laboratory tests address growth origin.
Failure to find curved banding is not a complete screen for all synthetic methods.
02 · TESTS & ULTRAVIOLET
What a test can—and cannot—tell you.
Results depend on the specimen, instrument and method. This is a reference for understanding evidence, not a home authentication or treatment verdict.
UV reaction
- Long-wave UV
- In a study of Madagascar metamorphic blue sapphires, unheated examples included both inert stones and stones with weak-to-moderate zoned orange fluorescence.
- Short-wave UV
- Before heating, that study's samples were inert under shortwave UV. Some developed chalky-blue responses during the treatment study.
This is a documented sample set, not a response table for every sapphire color or source. Instrument sensitivity affected detection. An inert reaction does not prove a stone is unheated, and synthetic corundum can also show chalky fluorescence.
Microscopy and component-by-component properties
Whether the crown and pavilion belong to one material or to a bonded assemblage.
Reference observation. A separation plane and trapped bubbles in cement can reveal an assembled stone.
Limit. Measurements from one component do not establish the identity of another.
Growth and treatment assessment
Evidence from internal features, UV observations and infrared spectroscopy.
Limit. Published sapphire treatment research combines these methods; no one glow or spectral feature should be treated as a complete treatment verdict.
Real laboratory examples
Documented cases, not test results of the reference specimens shown on this page.
Two stones, two materials in each
GIA examined greenish-yellow doublets with synthetic-spinel crowns and synthetic-sapphire pavilions; microscopy exposed the joined construction.
The takeaway. A plausible result from one facet can belong to only part of a stone.
Use a qualified gemologist for identification work. Do not expose eyes or skin to UV sources, or perform scratch, heat, acid or solvent tests on a gemstone. Do not assume that an absent UV reaction rules a material out.
03 · TREATMENTS & CARE
Protect the stone you actually have.
Disclosed treatments, fractures and settings can change which cleaning methods are appropriate.
Check treatment before cleaning. GIA recommends only a damp cloth for fracture-filled, cavity-filled or dyed sapphire; some shallow diffusion-treated color can be lost through surface damage or recutting.
04 · SOURCES & SCOPE
Know where each fact comes from.
Original NumisTrends explanations with primary references. This is not a replacement for gemological training, a laboratory report, or the examination of your own stone.
Properties reviewed: 2026-09-07 · Identification notes reviewed: 2026-09-07
- gia.edu · sapphire ↗
- gia.edu · winter 2019 analytical methods geographic origin determination gemstones ↗
- gia.edu · sapphire care cleaning ↗
NumisTrends is independent of GIA, Gem-A and the museums cited. A matching property cannot by itself establish identity, natural versus laboratory-grown origin, treatment, geographic origin, grade or value.