How to tell if aquamarine is real
Real aquamarine is blue beryl, the species of emerald: hardness 7.5 to 8, two refractometer readings under 1.60. Blue topaz reads over 1.60; glass, spinel once.
To tell if aquamarine is real, confirm beryl: hardness 7.5 to 8, two close refractometer readings below 1.60 (GIA gives 1.577 to 1.583), and blue against near-colourless in a dichroscope. Blue topaz reads above 1.60; glass and synthetic spinel give one reading. A 20.00 g aquamarine weighs 12.65 g in water.
In short
- Real aquamarine is beryl. GIA calls it the green-blue to blue variety of the mineral beryl, the species that also includes emerald. The Handbook beryl sheet gives hardness 7.5 to 8, density 2.63 to 2.97 and uniaxial negative optics. Aquamarine has no IMA row; beryl does.
- The 1.60 line. On a refractometer, aquamarine gives two readings, 1.577 to 1.583 on GIA’s figures and 1.567 to 1.590 on the International Gem Society’s. Blue topaz gives two readings above 1.60: the gem society’s blue topaz row reads 1.610 and 1.62. Glass and spinel give one reading, glass anywhere from 1.470 to 1.700 and spinel near 1.718 to 1.728.
- Blue topaz is the mineral impostor. The gem society says dark blue treated topaz is sometimes used as a simulant for aquamarine. A 20.00 g piece reads 12.65 g in water as aquamarine and 14.27 to 14.40 g as topaz. GIA’s gem identification course says synthetic light blue spinel, not synthetic aquamarine, often substitutes for aquamarine in inexpensive birthstone jewellery.
- The dichroscope checks the colour, not just the stone. GIA says aquamarine looks near colourless and stronger blue in different crystal directions. Spinel and glass show no pleochroism on the gem society’s pages, and nor does Maxixe beryl, an irradiated deep blue beryl the gem society says was not colour-stable.
- Real usually means heated. GIA says most aquamarine on the market was heat-treated to give a purer blue; the gem society puts the green tint’s disappearance at 375 °C and calls the heating undetectable. Synthetic aquamarine exists too: Schmetzer, in Gems & Gemology in 1990, measured one with indices and density inside the natural range.
| What it could be | Source | Refractometer readings | Against the 1.60 line | Dichroscope | Hardness | 20.00 g piece in water |
|---|---|---|---|---|---|---|
| Aquamarine | GIA; IGS | Two: 1.577 to 1.583 (GIA); 1.567 to 1.590 (IGS) | Below | Near colourless and stronger blue (GIA) | 7.5 to 8 | 12.65 g (GIA 2.72); 12.48 to 12.86 g (IGS 2.66 to 2.80) |
| Beryl, all colours | Handbook beryl sheet | Two: 1.565 to 1.610, rising with alkalis | Below, except alkali-rich beryl near 1.61 | Weak to distinct; O and E colours differ | 7.5 to 8 | 12.40 to 13.27 g |
| Maxixe beryl | IGS | As beryl | Below | None: blue in both windows (IGS) | As beryl | As beryl |
| Synthetic aquamarine | Schmetzer 1990 (GIA journal) | Two: 1.575 and 1.583 | Below: passes | Not separated here | Not given | 12.57 g (measured SG 2.69) |
| Blue topaz | Topaz sheet; IGS blue rows; GIA | Two: 1.606 to 1.644 (sheet); 1.610 and 1.62 (IGS blue) | Above | Pale blue: bright blue, pale rose, colourless (IGS) | 8 | 14.27 to 14.40 g |
| Synthetic spinel | GIA course sample; GIA lab note | One: 1.728 in the lab note | Above, single | None (IGS spinel: no pleochroism) | Not given | Not worked: no fetched density |
| Natural spinel | GIA spinel page | One: 1.718, singly refractive | Above, single | None (IGS) | 8 | 14.44 g (SG 3.60) |
| Glass | IGS glass article | One: anywhere from 1.470 to 1.700 | Either side, single | None (IGS) | 5 to 6 | 11.30 to 15.56 g |
How to tell if aquamarine is real: six checks, in order
Start with a lens and a dichroscope; finish, if you must, at a gem laboratory. The Handbook of Mineralogy beryl sheet supplies the species numbers: Be3Al2Si6O18, hexagonal, hardness 7.5 to 8, density 2.63 to 2.97 rising with alkali content, uniaxial negative, imperfect cleavage on {0001}. GIA’s aquamarine figures sit inside them: indices 1.577 to 1.583, specific gravity 2.72.
- Form, if it is a crystal. GIA describes six-sided prismatic crystals. A hexagonal prism on matrix is beryl-shaped; topaz on its sheet is orthorhombic, with vertically striated prisms.
- Lens. Round bubbles and swirl marks point to glass, on the gem society’s glass article.
- Dichroscope. Aquamarine shows near colourless in one window and stronger blue in the other, says GIA. Both windows the same blue is the warning.
- Refractometer. Apply the 1.60 line, below.
- Scale, for loose stones and rough. A 20.00 g aquamarine reads 12.65 g in water; topaz 14.27 g or more. Method: how to measure specific gravity at home. Hardness tests are for rough only, never a cut stone; see how to test mineral hardness properly.
- Laboratory, for synthetic aquamarine, which the gem society says professional laboratories can separate with advanced instruments.
The finish state is one of four labels: beryl, aquamarine (treatment unknown); blue topaz; singly refractive imitation, glass or spinel; or untested. The identification pages are indexed at the collecting guides.
Is my aquamarine real or blue topaz? The 1.60 line
The 1.60 line: two refractometer readings below 1.60 mean beryl; two above it mean topaz; a single reading means neither. GIA gives aquamarine 1.577 to 1.583 and the gem society 1.567 to 1.590. The topaz sheet prints 1.606 to 1.644; the International Gem Society topaz article gives its blue row, from the Tarryall Mountains, Colorado, as 1.610 and 1.62, and GIA gives topaz 1.619 to 1.627. The gap between aquamarine’s highest published reading, 1.590, and that blue topaz’s lower one is 0.020.
Where the line needs care. The Handbook beryl sheet’s full range runs to ω 1.610, increasing with alkali content, which touches topaz’s lowest 1.606. That high end belongs to alkali-rich beryl rather than to GIA’s aquamarine figures, but a reading between 1.60 and 1.61 should be settled by the optic character: beryl is uniaxial negative, topaz biaxial positive. A worn or curved surface gives no clean reading at all.
Weight agrees, when the stone is loose. A 20.00 g piece reads 12.65 g in water at GIA’s 2.72 and 14.27 to 14.40 g as topaz, a gap of at least 1.62 g; even the heaviest beryl on the sheet, 2.97, reads 13.27 g. At 5 ct the aquamarine-to-topaz gap is 0.081 g, worked, which a 0.01 g scale can show only with care. The gem society says treated dark blue topaz is sometimes passed off as aquamarine; the topaz side, including how blue topaz is made, is on topaz.
Synthetic spinel, glass and synthetic aquamarine: the imitations
Synthetic spinel is the imitation GIA names. Its GIA gem identification course sample says most inexpensive birthstone jewellery is set with imitations of synthetic corundum or synthetic spinel, and that synthetic light blue spinel, rather than synthetic aquamarine, often substitutes for natural aquamarine. Spinel is singly refractive, cubic, with no pleochroism; GIA gives natural spinel 1.718 and a GIA lab note reads synthetic spinel at 1.728. One reading, above the 1.60 line, and the same blue in both dichroscope windows: not beryl.
Glass gives one reading anywhere from 1.470 to 1.700, on the gem society’s figures, so it can land inside aquamarine’s window. It still gives only one reading and no pleochroism, and its specific gravity, 2.30 to 4.50, makes the scale useless against it. General imitations are on how to tell if a crystal is fake.
Synthetic aquamarine is the documented negative. Schmetzer, writing in GIA’s journal in 1990, described a hydrothermally grown synthetic aquamarine from Novosibirsk with indices 1.583 and 1.575 and a measured specific gravity of 2.69, inside the range for natural aquamarine, and noted there was then no commercial production. It passes the refractometer and the scale; the 1.60 line cannot catch it. The emerald variety of the same species has its own look-alike page, is dioptase the same as emerald.
Heated and irradiated aquamarine: real, but treated
Most aquamarine sold is heated, and it is still aquamarine. The GIA aquamarine quality factors page says most of the aquamarine on the market was heat-treated to give a purer blue, and the GIA description says heat usually gives a more bluish appearance. The International Gem Society aquamarine article puts the green tint’s disappearance at 375 °C, calls the heating very common and undetectable, and says graders should describe pure blue stones as probably heat treated. No home test sees it, and this page gives no heat test.
Maxixe beryl is the treated stone that the dichroscope catches. The gem society describes it as an irradiated, very dark blue beryl of the 1970s whose colour was not stable, and says it shows no pleochroism: both dichroscope windows stay blue, where natural aquamarine shows blue and colourless. It also notes that non-aquamarine beryls may be irradiated to match aquamarine colours.
Where fine beryl comes from is on the beryl page; the Handbook beryl sheet names, among others, Teófilo Otoni, Governador Valadares and Conselheiro Pena in Minas Gerais. This page gives no buying advice. Nothing on this site is offered for sale; the wanted list is the only commercial route.