GEMSTONE FIELD GUIDE
Andradite
Calcium-iron garnet; demantoid is its green gem variety, not a separate species. Natural compositions can grade toward grossular.
Microscopic view of inclusions in a faceted demantoid, the green variety of andradite garnet.
The photographer identifies this as demantoid and the curved fibers as byssolite. The scale belongs to this image; the feature alone does not establish geographical origin.
Dr Anatoly / CC BY 4.0, via Wikimedia Commons · Source ↗ · CC BY 4.0 · resized for the webA verified 3D specimen capture is not available for this entry. No generated stand-in is used.
AT A GLANCE
Start with the evidence.
Look closely at the real reference specimen, then compare several properties. Appearance or one matching test cannot confirm identity.
- Refractive index (RI)
- 1.880–1.895
- Specific gravity (SG)
- 3.8–3.9
- Mohs hardness
- 6.5–7
published gemological classification interval
How to read this value
From Stockton and Manson's 1985 GIA classification table; not a modern chemical species definition or a universal end-member interval. This lies beyond a standard approximately 1.80 gem refractometer: an over-range result is not a numerical measurement or an identification.
How to read this value
Handbook of Mineralogy measured mineral-reference interval, not an SG measured on a showcased gem. Gem-A separately gives approximately 3.8 for demantoid.
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 ↓Part of the garnet group. Read the group identification, tests and care guide → Each species keeps its own photographs and properties.
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)1.880–1.895
published gemological classification interval
From Stockton and Manson's 1985 GIA classification table; not a modern chemical species definition or a universal end-member interval. This lies beyond a standard approximately 1.80 gem refractometer: an over-range result is not a numerical measurement or an identification.
Specific gravity (SG)3.8–3.9
Handbook of Mineralogy measured mineral-reference interval, not an SG measured on a showcased gem. Gem-A separately gives approximately 3.8 for demantoid.
Mohs hardness6.5–7
Scratch resistance, not toughness. This ordinal scale is not linear.
BirefringenceNone intrinsically (ideal isotropic crystal)
The mineral reference notes that natural andradite is often weakly anomalously anisotropic.
Optic characterIsotropic / singly refractive (cubic)
CleavageNone
No true garnet cleavage; andradite is relatively softer than several other jewelry garnets.
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.
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.
No fluorescence color, negative reaction or identification procedure has been invented for this material. The reviewed properties and cited care information remain available.
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.
Demantoid may be heated to reduce a brown color component; this should not be generalized to all garnet species.
Rare garnet fracture filling is reported.
Use warm soapy water; avoid steam, hard blows and rough wear.
Fractured or filled gems require gentle cleaning.
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
- handbookofmineralogy.org · andradite.pdf ↗
- gia.edu · buyers guide ↗
- gia.edu · a proposed new classification for gem quality garnets.pdf ↗
- qcc.cuny.edu · garn.html ↗
- gia.edu · Gemstone Enhancement and its Detection in the 2000S.pdf ↗
- gia.edu · garnet 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.