GEMSTONE FIELD GUIDE
Diamond
A mineral species composed of carbon. Natural and laboratory-grown diamond must be distinguished by appropriate testing, not these basic constants.
The Uncle Sam diamond, NMNH G11741. Museum reference photograph; not NumisTrends inventory.
An emerald cut reveals long, stepped facets. This museum photograph is a reference, not an authentication or grading result.
Smithsonian National Museum of Natural History. Source-record image contributors: James D. Tiller, Brittany M. Hance and Timothy F. Reynolds. 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.
Separate two questions: is the material diamond, and did it grow naturally or in a laboratory? A convincing appearance does not answer both.
- Refractive index (RI)
- 2.42
- Specific gravity (SG)
- 3.51–3.53 · typical 3.52
- Mohs hardness
- 10
typical single value
How to read this value
GIA rounds the single refractive index to 2.42; no RI range is stated on this overview. Singly refractive in the ideal strain-free crystal.
How to read this value
Bounds are arithmetic expansion of GIA's 3.52 ± 0.01; not measurements of a featured diamond.
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)2.42
typical single value
GIA rounds the single refractive index to 2.42; no RI range is stated on this overview. Singly refractive in the ideal strain-free crystal.
Specific gravity (SG)3.51–3.53 · typical 3.52
Bounds are arithmetic expansion of GIA's 3.52 ± 0.01; not measurements of a featured diamond.
Mohs hardness10
Scratch resistance, not toughness. This ordinal scale is not linear.
BirefringenceNone (0 in the ideal strain-free crystal)
Strain-related anomalous birefringence can occur; this is not intrinsic uniaxial/biaxial double refraction.
Optic characterIsotropic / singly refractive (cubic)
CleavagePerfect octahedral cleavage in four directions
High scratch hardness does not mean resistance to chipping or cleavage.
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 moissanite
A brilliant, durable diamond simulant.
How to investigate. A gemologist can assess its double refraction and use appropriate identification equipment.
Do not identify it from sparkle alone.
Cubic zirconia
A common manufactured diamond imitation.
How to investigate. Professional optical and physical testing separates the material from diamond.
Laboratory-grown diamond is not cubic zirconia; keep these identities separate.
Laboratory-grown diamond
It is diamond, with the same crystal structure, but a different growth origin.
How to investigate. Use validated screening followed by the indicated laboratory testing.
List as an origin distinction, not as a non-diamond imitation.
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
- Some diamonds fluoresce; blue is the most frequently reported color among fluorescent diamonds, while other colors occur. GIA report fluorescence describes the longwave response.
- Short-wave UV
- Fluorescent natural diamonds generally respond more strongly to longwave than shortwave UV; HPHT- and CVD-grown diamonds often show the opposite relationship.
These are tendencies, not origin verdicts. A non-fluorescent result does not prove natural growth. Deep-UV growth imaging is a separate laboratory technique, not interchangeable with the longwave response on a report.
Diamond identification and growth-origin screening
Whether the specimen is diamond rather than a simulant, followed by evidence of natural or laboratory growth.
Limit. Laboratory-grown diamond has the diamond crystal structure. Specialized screening and spectroscopic follow-up—not appearance alone—are used to establish its growth origin.
Magnified optical comparison
Optical differences between diamond and lookalike materials.
Reference observation. Moissanite can show doubled images of back-facet edges because it is doubly refractive.
Limit. Treat this as a professional comparison clue, not a photograph-based pass/fail test.
Real laboratory examples
Documented cases, not test results of the reference specimens shown on this page.
One laboratory-grown diamond, two UV observations
GIA illustrates a laboratory-grown diamond with no visible longwave glow but a shortwave response.
The takeaway. A longwave-only observation can miss information relevant to screening.
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.
Avoid abrasives and bleach when cleaning diamond jewelry. Ask a jeweler before ultrasonic cleaning: inclusions, fracture filling, and the setting can change what is safe.
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 · diamond ↗
- gia.edu · SU12.pdf ↗
- gia.edu · spring 2015 visible absorption spectra of colored diamonds ↗
- gia.edu · how protect diamond chipping ↗
- 4cs.gia.edu · ↗
- gia.edu · diamond 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.