Aquamarine

Description

Aquamarine is a blue to blue-green variety of the mineral beryl. Its name is derived from the Latin 'aqua marina', meaning 'water of the sea', referring to its ocean-like color. It is a cyclosilicate mineral with a hexagonal crystal system, often forming well-developed prismatic crystals. The color can range from very pale, almost colorless blue to a deep, vibrant blue, with the latter being more valuable. It is known for its excellent transparency and vitreous luster.

How to Identify

Color

Ranges from pale blue to deep blue-green. The color is typically uniform, though some zoning can occur. The most prized color is a deep, saturated blue.

Luster

Vitreous (glassy).

Texture

Smooth to the touch on crystal faces; conchoidal fracture surfaces are smooth and curved.

Crystal Form

Typically forms hexagonal prisms, often with flat pinacoid terminations. Crystals can be columnar, massive, or granular. Striations parallel to the c-axis are common on prism faces.

Cleavage

Imperfect basal cleavage (0001), often not observed in hand specimens or fractured pieces.

Geological Environment

Found primarily in granitic pegmatites, especially those rich in lithium and tin. Also occurs in hydrothermal veins and in alluvial deposits derived from these primary sources.

Key Facts

• Hardness: 7.5-8 on the Mohs scale
• Specific Gravity: 2.68-2.80 g/cm³
• Crystal System: Hexagonal
• Color: Blue to blue-green
• Luster: Vitreous
• Transparency: Transparent to translucent
• Fracture: Conchoidal to uneven
• Cleavage: Imperfect basal (0001)
• Composition: Beryllium aluminum cyclosilicate (Be3Al2Si6O18)

Quick Check

• Color: Blue to blue-green
• Luster: Vitreous
• Streak: White

Physical Characteristics

• Crystal Habit: Prismatic, columnar, massive, granular. Often forms well-developed hexagonal prisms, sometimes with striations parallel to the c-axis.
• Cleavage Type: Imperfect on {0001}. Typically not a prominent feature and rarely observed in fractured specimens.
• Fracture Type: Conchoidal to uneven. Breaks with smooth, curved surfaces or irregular, rough surfaces.
• Tenacity: Brittle. It will break or chip under impact.
• Luster Type: Vitreous (glassy). Some specimens may exhibit a resinous luster on fracture surfaces.

Formation

Aquamarine forms in pegmatites, which are coarse-grained igneous rocks, and in hydrothermal veins. It crystallizes from beryllium-rich, silica-saturated fluids at elevated temperatures and pressures. The characteristic blue-green color is due to trace amounts of ferrous iron (Fe2+) substituting for aluminum in the beryl crystal structure. The intensity of the blue color can be enhanced by heat treatment, which converts Fe3+ to Fe2+.

Usage

Primarily used as a gemstone in jewelry due to its attractive blue-green color, transparency, and hardness. Larger, high-quality crystals are highly prized. It is also a source of beryllium, though other beryl varieties or minerals like bertrandite are more commonly mined for industrial beryllium extraction.

Age Distribution

Formed in various geological eras, often associated with granitic intrusions from the Precambrian to the Cenozoic.

Where to Find

Finding Tips

Similar Rocks

Scientific Classification

Mineral Class

Silicates

Group

Beryl Group (Cyclosilicates)

Crystal System

Hexagonal (Dihexagonal-dipyramidal class)

Chemical Formula

Be3Al2Si6O18

Composition

Beryllium aluminum cyclosilicate. Trace amounts of ferrous iron (Fe2+) cause the blue color. Other minor impurities can include alkali metals (Na, K, Cs) and water.

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