The open encyclopedia of minerals
GlossaryCite the database
Mineralogist.org
Minerals A–ZSearchCollectionsBrowse by PropertyIdentify a SpecimenCompare MineralsLocalities MapGlossaryContribute Search the Database →
Variety · Silicate · Cyclosilicate (ring silicate) · Beryl Group · of Beryl

Aquamarine

Be₃Al₂Si₆O₁₈

Beryl in sea-blue — iron instead of chromium gives this sister of emerald its clear ocean color. March’s birthstone.

Hardness7.5–8
Crystal systemHexagonal
LusterVitreous
Sp. gravity2.66–2.74
ClassSilicate
←PrevAqualiteNextAradite→
Aquamarine specimen

Aquamarine prisms — the sea-blue variety of beryl — Photo: Robert M. Lavinsky · CC BY-SA 3.0

What is Aquamarine?

Aquamarine is the blue to blue-green variety of beryl — the same Be₃Al₂Si₆O₁₈ mineral as emerald, colored by iron instead of chromium. Its name is literal Latin: aqua marina, ‘water of the sea’.

Where emerald is rare and included, aquamarine grows big and clean. Pegmatite pockets have yielded gem crystals weighing tens of kilograms — Brazil’s famous 1936 find was a flawless prism the size of a forearm — and faceted stones of hundreds of carats exist. It is the birthstone for March and the most popular blue gem after sapphire.

Many aquamarines began life greener than they look: a gentle heat treatment drives off the yellow component and leaves pure sea-blue.

In one sentence: Aquamarine is a hexagonal beryl prism — hardness 7.5–8, glassy luster — in every shade of seawater, from pale sky to the prized deep ‘Santa Maria’ blue.

Physical Properties

The full data table is in the panel alongside. Here’s what those numbers actually mean.

Color. Trace iron does the work: Fe²⁺ gives the blue, while Fe³⁺ adds a yellow tint that pushes the stone toward green or ‘seafoam’. Heating to about 400 °C removes the yellow — which is why most jewelry-grade aquamarine is pure blue.

Size and clarity. Unlike its sister emerald, aquamarine commonly forms large, eye-clean crystals — the gem-cutter’s dream. Inclusions, when present, are usually fine parallel hollow tubes called ‘rain’, or liquid feathers.

Optics. Uniaxial negative, refractive index ~1.57–1.59, with weak-to-distinct pleochroism: a well-oriented rough shows deeper blue down the crystal’s length, and cutters orient the table to keep it.

How & Where It Forms

Aquamarine crystallizes inside granitic pegmatites — the coarse, giant-crystal rocks that form as the last water-rich dregs of a cooling granite. Beryllium concentrates in those late fluids, and where open pockets (miaroles) exist, beryl prisms can grow to spectacular size.

Weathering then frees the crystals. Because beryl is hard and chemically stable, aquamarine also accumulates in river and alluvial gravels downstream of eroded pegmatites — Brazil’s Minas Gerais gem belt works both kinds of deposit.

Often grows alongside:

QuartzMicroclineMuscoviteTopazTourmalineCassiterite

What It’s Used For

Fine gemstonesThe March birthstone; hard enough for everyday rings. Most stones are heat-treated to pure blue.
Collector specimensGemmy prisms on feldspar and muscovite matrix — Pakistan’s Shigar Valley sets the modern standard.
Historical talismanRoman sailors carried aquamarine against storms — the ‘sailor’s gem’.

How to Identify It

The combination of hexagonal prisms, hardness 7.5–8 and pale-to-mid blue color is nearly diagnostic. Blue topaz is the commonest lookalike — it is noticeably heavier (SG ~3.5), has a higher refractive index and one perfect cleavage. Blue zircon is far denser and flashes strong doubling of facet edges under a loupe.

Hardness 7.5–8 — scratches glass, isn’t scratched by steelSix-sided (hexagonal) prism habitWeak dichroism — colorless one way, blue the otherOften flawless or with fine parallel hollow-tube inclusions
Looks like…But differs because…Quick test
TopazDenser (SG ~3.5), higher refractive index (~1.62) and one perfect cleavageCleavage & SG
ZirconFar denser (~4.7) with strong doubling of facet edges and adamantine lusterHeft & loupe
SpinelCubic and singly refractive; synthetic blue spinel is a common simulantPolariscope
ApatiteMuch softer (5) — a knife blade marks itHardness

Where It’s Found

Notable localities for fine specimens:

Santa Maria de Itabira, Brazil Shigar Valley, Skardu, Pakistan Erongo Mountains, Namibia Mount Antero, USA Mursinka, Ural Mountains, Russia Central Highlands, MadagascarOpen the locality map →

References & Further Reading

  1. Dana’s New Mineralogy, 8th ed. Beryl group, cyclosilicates.
  2. Mindat.org — Aquamarine variety data and locality records.
  3. Wikipedia — Aquamarine (gem).

Last reviewed 2026-09-14 · How to cite this page.