Input Sections
A complete reference for all 15 measurement and observation sections in the GemID identification screen.
GemID has 15 measurement and observation sections, each mapping to a standard gemological test. Expand any section by tapping its header on the identification screen. You don't need data for every section — even 3 to 4 well-chosen measurements typically narrow the candidate list to 2 to 5 gems.
Recommended sequence: Start with what you can observe without instruments (color, transparency, luster). Then measure refractive index — it eliminates the most candidates of any single test. Follow with specific gravity to confirm. Use fluorescence, optic character, and spectroscope for final disambiguation.
01 Visual Observations
What it measures
Color category, transparency, and luster — the three properties observable with the naked eye before any instrument is used.
- Color category: Colorless, red/pink, blue/violet, green, yellow/orange, brown, purple, black, color-change, multi-color. Multiple categories can be selected.
- Transparency: Transparent, translucent, or opaque. Select one.
- Luster: Vitreous, adamantine, resinous, waxy, metallic, pearly, or silky. Select one.
When to use it
Always. Enter visual observations first — they require no equipment and immediately constrain the candidate list.
How to enter it in GemID
Tap color chips to select one or more color categories. Tap a single transparency option and a single luster option. Selections are highlighted when active; tap again to deselect.
What it eliminates
- Color category eliminates all gems outside the selected color families. Selecting blue/violet alone removes more than half the database.
- Adamantine luster strongly indicates diamond, zircon, cassiterite, or demantoid garnet — most common vitreous-luster stones are ruled out.
- Opaque eliminates all transparent faceted stones (corundum, beryl, topaz, quartz, etc.).
- Metallic luster limits candidates to hematite, pyrite, and a small set of metallic minerals.
02 Loupe Observations
What it measures
Whether inclusions are visible at 10x magnification, and any free-text notes about what you observe.
When to use it
Examine the stone with a 10x loupe in good lighting. Note whether inclusions, crystals, needles, silk (rutile needles), fingerprints (healed fractures), clouds, or growth zoning are visible.
How to enter it in GemID
Toggle inclusion presence to Yes, No, or Unknown. Use the notes text field to record what you see. Notes are for your records and appear in saved sessions and reports; they are not used in the real-time filtering logic.
What it eliminates
Loupe observations are not directly applied to filter candidates in real time. However, recorded inclusion notes are factored into natural vs. synthetic testing — for example, curved growth striae visible under the loupe are characteristic of flame-fusion synthetics, while fingerprint inclusions suggest natural origin.
Tip: Even if you don't record detailed notes here, use this section to log your loupe findings before moving to the polariscope or refractometer. Detailed loupe notes add significant value to saved examination records and reports.
03 Darkfield / Loupe
What it measures
Observations made under darkfield illumination, and facet doubling — the visible doubling of back facet edges when viewed through the table of a faceted stone.
When to use it
Use a loupe under darkfield illumination (light from the side, dark background). Facet doubling is most easily seen by looking straight down through the table facet toward the back facets with strong magnification.
How to enter it in GemID
Toggle facet doubling to Yes or No. Use the free-text field to record additional darkfield observations such as clarity features visible only under darkfield conditions.
What it eliminates
- Facet doubling Yes: Eliminates all SR stones (garnet, spinel, diamond, glass, CZ) and low-birefringence DR stones. Strongly points to zircon, peridot, or sphene.
- Facet doubling No: Rules out high-birefringence stones like zircon and peridot in most faceted cuts.
04 Lighting Effects
What it measures
Whether the stone exhibits a color change under different light sources, and any special optical phenomena.
- Color change: Yes or No. A stone that appears one color in daylight/fluorescent light and a clearly different color under incandescent light.
- Special phenomena: Asterism (star), chatoyancy (cat's eye), adularescence (moonstone glow), labradorescence (color play in labradorite), play-of-color (opal-type spectral flash), or none.
When to use it
View the stone under both daylight or cool-white fluorescent light and a warm incandescent or halogen source to check for color change. For phenomena, use a fiber optic or focused penlight moving across the surface.
How to enter it in GemID
Toggle color change yes or no. Select one phenomenon from the chip row, or leave at "none" if no phenomenon is present.
What it eliminates
- Color change Yes: Limits candidates to alexandrite, color-change garnet, color-change sapphire, color-change spinel, and diaspore. Eliminates the vast majority of the database.
- Asterism: Keeps star ruby, star sapphire, star garnet, star diopside, and star rose quartz. Eliminates all non-asteriated stones.
- Chatoyancy: Keeps cat's eye chrysoberyl, tiger's eye, hawk's eye, cat's eye tourmaline, and cat's eye apatite.
- Play-of-color: Keeps precious opal varieties only.
- Labradorescence: Keeps labradorite and spectrolite.
- Adularescence: Keeps orthoclase moonstone and adularia.
05 Polariscope
What it measures
Optic character — whether the stone is singly refractive (SR) or doubly refractive (DR) — and if DR, the optic sign (uniaxial or biaxial, positive or negative). An anomalous DR toggle covers strain-related double refraction in otherwise SR stones.
When to use it
Use a polariscope or two polaroid filters crossed at 90 degrees. Rotate the stone between the polars through a full 360-degree rotation.
- SR: Stone remains dark throughout the full rotation (isometric crystal system or amorphous).
- DR: Stone blinks light and dark, going through four cycles of extinction per full rotation.
- Anomalous DR: An otherwise SR stone shows patchy, irregular light — caused by strain. Common in garnets and glass.
To determine optic sign (uniaxial vs. biaxial), use a conoscope or interference figure technique — observe the stone's optic axis figure through the polariscope.
How to enter it in GemID
Select SR or DR. If DR, select the optic sign or choose "unknown" if you can't determine the sign. Toggle anomalous DR if the stone shows anomalous double refraction.
What it eliminates
- SR: Keeps garnet (all types), spinel, diamond, glass, cubic zirconia, opal, fluorite, sphalerite, amber, moldavite, and obsidian. Eliminates quartz, corundum, beryl, tourmaline, topaz, and all other DR species.
- DR Uniaxial: Keeps quartz, corundum (ruby, sapphire), tourmaline, beryl (emerald, aquamarine, morganite), apatite, and other trigonal/hexagonal/tetragonal species.
- DR Biaxial: Keeps topaz, chrysoberyl, orthoclase, labradorite, peridot, andalusite, and other orthorhombic/monoclinic/triclinic species.
06 Refractometer
What it measures
The refractive index (RI) — the ratio of light speed in a vacuum to light speed in the gem material. RI min and RI max for DR stones; a single value for SR stones. Measured with a gemological refractometer and contact liquid (RI approximately 1.81).
When to use it
Use on any faceted stone with a flat, polished surface. The refractometer is the single most important instrument for gem identification. A flat facet is required — curved or rough surfaces require a spot reading technique.
How to enter it in GemID
Enter RI min and RI max as decimal values (e.g., 1.762 and 1.770 for ruby). For a single reading on an SR stone, enter the same value in both fields or enter just the min. Check Spot reading if the reading was taken from a curved surface — GemID uses a wider tolerance for spot readings.
What it eliminates
- RI 1.760–1.770 → corundum family (ruby, sapphire, star ruby, star sapphire)
- RI 1.543–1.553 → quartz family (amethyst, citrine, smoky quartz, rose quartz, rock crystal)
- RI 1.925–1.984 → zircon (high type)
- RI 1.654–1.690 → peridot
- RI 1.740–1.760 → spinel range (overlaps with lower corundum)
See the RI reference chart for a full list of gem RI ranges.
07 Density / SG
What it measures
Specific gravity (SG) — the ratio of the gem's weight in air to the weight of an equal volume of water. Measured by hydrostatic weighing (weight in air minus weight in water).
When to use it
After RI. Together, RI and SG are the most powerful two-measurement combination in gemology — they identify the vast majority of transparent faceted stones unambiguously. SG requires a loose stone for accurate results.
How to enter it in GemID
Enter the calculated SG as a decimal value. If the stone is set in a mounting, toggle In setting — a warning banner appears in the Results panel indicating that SG may be unreliable, and the measurement is given reduced weight in the filtering logic.
What it eliminates
- Ruby (SG ~4.00) vs. red spinel (SG ~3.52) — same red color, overlapping RI range, SG distinguishes them cleanly.
- Diamond (SG 3.52) vs. CZ (SG 5.60–5.95) — both SR, both high RI, but SG is drastically different.
- Topaz (SG 3.49–3.57) vs. aquamarine (SG 2.68–2.74) — overlapping color, very different density.
See the SG measurement guide for hydrostatic weighing instructions.
In setting: Hydrostatic weighing is not possible on a mounted stone. The "In setting" toggle suppresses the SG warning in the Results panel and reduces the weight given to the SG value in filtering. If you can estimate SG from the mounting weight, enter it as a rough guide only.
08 Dichroscope
What it measures
Pleochroism — whether the stone shows different colors when viewed along different optical axes. Strength (none, weak, moderate, strong) and a trichroic toggle for stones showing three distinct colors.
When to use it
Use a calcite-plate dichroscope or polaroid dichroscope. View the stone from multiple directions, rotating the dichroscope at each position. Look for two windows in the dichroscope showing different colors simultaneously.
How to enter it in GemID
Select pleochroism strength from the four-option chip row. If three distinct colors are visible when the stone is viewed from different directions (not just two), toggle Trichroic on.
What it eliminates
- Strong pleochroism: Strongly indicates tourmaline (often very strong), tanzanite/zoisite, iolite/cordierite, or alexandrite.
- Trichroic: Limits candidates to orthorhombic, monoclinic, and triclinic species — andalusite, tanzanite, iolite, and orthoclase are characteristic. Confirms biaxial character.
- None: Consistent with SR stones (garnet, spinel, diamond) and all directions of isometric crystals, but also some DR stones viewed along an optic axis.
- SR stones physically cannot show pleochroism — strong pleochroism rules out all isometric and amorphous gem materials.
09 Chelsea Filter
What it measures
Whether the stone appears red, green, or neither ("weak") when viewed through the Chelsea filter — a dichroic filter that transmits only deep red and yellow-green wavelengths.
When to use it
View the stone under a strong incandescent or halogen light source (not fluorescent or daylight LED). Hold the filter close to your eye and view the stone at arm's length. The stone will appear either red, green, or a weak/neutral reaction.
How to enter it in GemID
Select Red, Green, or Weak from the three-option chip row.
What it eliminates
- Red reaction: Indicates chrome or cobalt coloration. Red in Chelsea filter is characteristic of natural emerald (chrome), alexandrite, chrome tourmaline, ruby, red spinel, and some synthetic blue stones dyed with cobalt.
- Green reaction: Indicates no significant chrome or cobalt absorption in the deep red. Common in aquamarine, blue topaz, synthetic emerald (many), blue glass, and most non-chrome green stones.
- Weak/neutral: Neither strong red nor strong green — many colorless and pale stones, as well as stones with complex absorption spectra.
See the Chelsea filter guide for technique and a full reaction table.
Note: The Chelsea filter was originally developed to separate natural from synthetic emerald, but that use case no longer holds — many synthetic emeralds also react red. It remains useful for detecting chrome and cobalt coloration in unknown stones.
10 Hanneman Filter
What it measures
Reaction to the Hanneman-Hodgkinson filter set — a group of filters designed to detect specific treated and synthetic gem materials that the Chelsea filter alone cannot distinguish.
When to use it
Use in the same manner as the Chelsea filter: strong incandescent light, filter held to the eye. The Hanneman filter is optimized for detecting synthetic blue spinel (cobalt-colored), aquamarine simulants, tanzanite simulants, and certain treated blue diamonds.
How to enter it in GemID
Select Positive or Negative reaction.
What it eliminates
- Positive reaction: Strongly indicates synthetic blue spinel colored by cobalt, or certain other cobalt-doped synthetics. A positive Hanneman result in a blue stone is a significant flag for synthetic or treated material.
- Negative reaction: Consistent with natural aquamarine, blue sapphire, blue topaz, iolite, and most natural blue stones. Does not rule out synthetic corundum.
11 Spectroscope
What it measures
Absorption lines and bands in the visible spectrum — diagnostic features caused by specific chromophore elements (chrome, iron, cobalt, manganese, copper, vanadium) in the gem material.
When to use it
Use a diffraction grating spectroscope or a prism spectroscope. View the stone in transmitted or reflected light against a strong incandescent or fiber optic source. Dark vertical lines or bands at specific wavelength positions are the target observations.
How to enter it in GemID
Tap the chip for each absorption band you observe. Available chips: 450 nm, 480 nm, 520 nm, 580–590 nm, 650 nm, 687 nm, 693 nm. Use the notes field to record any additional bands not covered by the chips.
What it eliminates
- 687 nm + 693 nm doublet: Diagnostic for ruby, red spinel, and pyrope garnet — chromium doublet in red stones.
- 687 nm alone: Characteristic of chrome tourmaline, emerald, and alexandrite.
- 450 nm band: Strongly indicative of blue glass, synthetic blue corundum (cobalt-colored), or blue spinel.
- 580–590 nm double band: Characteristic of cape-series yellow diamonds (nitrogen-related absorption).
- 520 nm: Demantoid garnet (andradite); also present in some chrome diopside.
- 480 nm: Present in blue zircon and some aquamarine.
Note: Spectroscope observation takes practice. Start with well-known reference stones to calibrate your eye before relying on spectroscope results in identification. Absorption bands are easier to see in deeply colored stones.
12 UV Fluorescence
What it measures
The stone's fluorescence under longwave UV (LW, 365 nm) and shortwave UV (SW, 254 nm). For each, enter strength (inert, weak, moderate, strong) and color.
When to use it
In a darkened room. Test LW first — it's safer and more commonly observed. For SW, wear UV-protective eyewear; shortwave UV is harmful to eyes and skin with prolonged exposure.
How to enter it in GemID
Select fluorescence strength for longwave UV. If the stone fluoresces, tap the color swatch to set the fluorescence color. Repeat for shortwave UV. If the stone shows no fluorescence under either wavelength, select "Inert" for both.
What it eliminates
- Strong chalky white LW: Highly characteristic of flame-fusion (Verneuil) synthetic corundum. Natural corundum may fluoresce red or be inert — chalky white is a synthetic flag.
- LW blue: Common in natural diamond (type IaA). Also seen in some fluorite, scheelite, and calcite.
- LW red / pink: Ruby, pink sapphire, spinel, alexandrite, and chrome tourmaline. The red is from chromium fluorescence.
- LW orange: Hessonite garnet, some topaz, some amber.
- Inert under both: Common in aquamarine, blue sapphire, emerald, and most dark-colored stones, but not diagnostic on its own.
- SW stronger than LW: Can indicate synthetic flux-grown emerald in some cases.
See the UV fluorescence guide for a complete reaction table by gem species.
13 Thermal Reaction
What it measures
Whether the stone conducts heat at the rate characteristic of diamond (and moissanite), as measured by an electronic thermal conductivity tester (diamond tester).
When to use it
Touch the probe tip to a flat, clean facet — the table facet is ideal. The tester measures the rate at which heat from the probe tip conducts into the stone. Diamond and moissanite both conduct heat far faster than any other common gem material.
How to enter it in GemID
Select Reacts (indicator lights up / alarm sounds) or Does not react.
What it eliminates
Important: Moissanite also reacts positively on most standard diamond testers. A positive result from a colorless stone does not confirm diamond. Use a dedicated moissanite tester or check RI — moissanite reads above 2.65, off the scale of most standard gemological refractometers — to distinguish the two.
- Reacts: Candidate list limited to diamond and moissanite. Combined with RI and SG, diamond vs. moissanite is definitively resolved.
- Does not react: Eliminates diamond and moissanite. The stone is something else — continue with RI and other tests.
14 Magnetism
What it measures
Whether the stone is attracted to a strong magnet — indicating the presence of iron, nickel, or other magnetic elements in inclusions or the gem material itself.
When to use it
Use a rare earth (neodymium) magnet — a standard refrigerator magnet is not strong enough for weak attraction. Suspend the stone on a thin thread or place it on a smooth non-ferrous surface and approach the magnet slowly from the side.
How to enter it in GemID
Select Strong attraction, Weak attraction, or Inert.
What it eliminates
- Strong attraction: Characteristic of HPHT-grown synthetic diamond (contains iron-nickel flux inclusions), some demantoid garnet (contains iron-bearing horsetail inclusions), hematite, magnetite, and metallic pyrite. Strongly magnetic natural corundum is known but rare.
- Weak attraction: Some almandine and pyrope garnets (high iron content), some rare manganese-rich stones. Weak attraction in a red stone increases the probability of almandine garnet.
- Inert: The vast majority of gem species. Inert result does not significantly constrain the candidate list, but rules out strongly magnetic species.
15 Hardness
What it measures
Relative scratch hardness on the Mohs scale (1–10). Used as a supporting measurement — not a first-choice test for faceted gems, since scratch testing can damage polished surfaces.
When to use it
Use a hardness reference set, or use known objects as rough standards: fingernail (~2.5), copper coin (~3.5), steel penknife blade (~5.5), steel file (~6.5), quartz (~7), topaz (~8), corundum (~9). Apply only to an inconspicuous surface — a girdle edge or a rough area — never to a polished facet on a client's stone.
How to enter it in GemID
Enter the approximate hardness value from your scratch test. If only a minimum is established (e.g., "harder than quartz, didn't test further"), enter just the min value. GemID uses the range to filter candidates.
What it eliminates
- Hardness below 7: Eliminates ruby, sapphire (corundum, 9), topaz (8), chrysoberyl (8.5), diamond (10), spinel (8), and most hard transparent faceted stones. Consistent with fluorite (4), apatite (5), orthoclase (6), peridot (6.5–7).
- Hardness 7–7.5: Consistent with quartz family, tourmaline, andalusite.
- Hardness 8–8.5: Consistent with topaz, spinel, chrysoberyl, beryl.
- Hardness 9: Corundum (ruby, sapphire) only, or very hard synthetic corundum.
- Hardness 10: Diamond only.
Use with caution on finished gems. Scratch testing is destructive on polished surfaces and is best reserved for rough material, unimportant girdle edges, or when other tests have been inconclusive and the identification stakes are low.