GEMSTONE FIELD GUIDE
Grossular
Calcium-aluminum garnet. Tsavorite and hessonite are varieties, not separate species. Scope is gem grossular, not every hydrogarnet or grossular-rich aggregate.
Grossular garnets in a range of colors, photographed in a National Museum of Natural History display.
A museum display illustrates a range of grossular garnet colors. A color alone is not enough to assign every stone a named variety.
Alkivar / Public domain, via Wikimedia Commons · Source ↗ · Public domain · 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)
- 1.73–1.75
- Specific gravity (SG)
- 3.4–3.8
- Mohs hardness
- 7–7.5 (gem-table reference)
rounded typical gem-material interval
How to read this value
Rounded gem-trade teaching interval. Composition and substitutions can extend optical constants beyond a headline interval.
How to read this value
Gem-A 2017 teaching interval; no midpoint invented. Not pure-end-member density.
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)1.73–1.75
rounded typical gem-material interval
Rounded gem-trade teaching interval. Composition and substitutions can extend optical constants beyond a headline interval.
Specific gravity (SG)3.4–3.8
Gem-A 2017 teaching interval; no midpoint invented. Not pure-end-member density.
Mohs hardness7–7.5 (gem-table reference)
Scratch resistance, not toughness. This ordinal scale is not linear.
BirefringenceNone intrinsically (ideal isotropic crystal)
Cubic in the ideal state; strain-related weak birefringence can occur.
Optic characterIsotropic / singly refractive (cubic)
An anomalous polariscope reaction, where present, must not be confused with ordinary uniaxial or biaxial double refraction.
CleavageNo true cleavage; rare parting
The mineral sheet records rare {110} parting, distinct from true cleavage. Mineral-reference hardness is 6.5–7, while the cited gem table gives 7–7.5; hardness is not an exact universal constant.
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.
Usually untreated; rare fracture filling is reported for garnets.
Use warm soapy water. Avoid steam, hard blows and rough wear; assess fractures before ultrasonic 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 · grossular.pdf ↗
- gem-a.com · ↗
- gem-a.com · Foundation in Gemmolgy Specifications and Syllabus.pdf ↗
- gia.edu · a proposed new classification for gem quality garnets.pdf ↗
- qcc.cuny.edu · garn.html ↗
- gia.edu · garnet care cleaning ↗
- gem-a.com · ↗
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.