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Aquamarine is a blue to blue-green variety of the mineral beryl. Its name is derived from the Latin words 'aqua marina', meaning 'water of the sea', referring to its ocean-like color. It is known for its excellent transparency and vitreous luster. Aquamarine crystals can grow to considerable sizes, often forming well-developed hexagonal prisms.
How to Identify
- Color
- Ranges from pale blue to deep blue, often with a greenish tint. The most valuable aquamarines are typically a clear, intense blue.
- Luster
- Vitreous (glassy).
- Texture
- Smooth to the touch when polished; rough on crystal faces.
- Crystal Form
- Typically forms hexagonal prisms, often with striations parallel to the c-axis. Can also be found as massive or granular aggregates.
- Cleavage
- Imperfect basal cleavage {0001}, rarely observed in practice due to its toughness.
- Geological Environment
- Found in granitic pegmatites, hydrothermal veins, and sometimes in alluvial deposits derived from these primary sources. Often associated with minerals like feldspar, quartz, muscovite, and other beryl varieties.
Key Facts
- Hardness: 7.5 - 8 on the Mohs scale
- Specific Gravity: 2.68 - 2.80 g/cm³
- Crystal System: Hexagonal
- Color: Pale blue to deep blue, often with a greenish tint
- 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, typically hexagonal, often elongated and striated parallel to the c-axis. Can also be massive or granular.
- Cleavage Type: Imperfect basal {0001}. Rarely observed in practice due to its toughness.
- Fracture Type: Conchoidal to uneven, brittle.
- Tenacity: Brittle
- Luster Type: Vitreous (glassy)
Formation
Aquamarine forms in pegmatites, which are coarse-grained igneous rocks, and in hydrothermal veins. It crystallizes from beryllium-rich magmatic fluids that cool slowly, allowing large crystals to grow. The characteristic blue-green color is due to trace amounts of ferrous iron (Fe2+) within the beryl crystal structure. Heat treatment can alter the color by changing the oxidation state of iron.
Usage
Primarily used as a gemstone in jewelry due to its attractive color, clarity, and hardness. Larger, high-quality crystals are highly prized. It is also collected by mineral enthusiasts.
Age Distribution
Formed during various geological periods, often associated with late-stage magmatic and hydrothermal activity, typically in granitic pegmatites and metamorphic rocks.
Where to Find
Minas Gerais, Brazil
One of the most significant sources, producing large, high-quality crystals.
Pakistan
Known for producing fine, often intensely colored aquamarine crystals, particularly from the Shigar Valley.
Nigeria
A notable producer of good quality aquamarine.
Madagascar
Produces aquamarine, sometimes with a distinct blue-green hue.
Russia (Ural Mountains)
Historically important source, particularly for older specimens.
United States (Colorado, California)
Smaller deposits, but some notable specimens have been found, particularly in Colorado's Mount Antero.
Finding Tips
Target Pegmatite Deposits
Focus your search on areas known for granitic pegmatites, as these are the primary geological environments for aquamarine formation. Look for exposed pegmatite dikes.
Look for Associated Minerals
Aquamarine often occurs with quartz, feldspar, muscovite, and sometimes tourmaline. Identifying these associated minerals can indicate the presence of beryl.
Check Alluvial Deposits
In areas downstream from primary sources, aquamarine crystals can be found in riverbeds and gravels due to their hardness and resistance to weathering.
Examine Crystal Habit
Look for characteristic hexagonal prismatic crystals. Even small fragments may show evidence of the hexagonal cross-section.
Consider Color and Luster
The distinctive blue to blue-green color and vitreous luster are key identifiers. Even in rough form, these properties can be noticeable.
Similar Rocks
Topaz
Topaz (variety Blue)
Also known as: Blue Topaz
Blue Zircon
Zircon (variety Blue)
Also known as: Starlite
Euclase
Euclase
Also known as: None
Kyanite
Kyanite
Also known as: Cyanite
Scientific Classification
- Mineral Class
- Silicates
- Group
- Cyclosilicates (Beryl Group)
- Crystal System
- Hexagonal (Dihexagonal-dipyramidal class)
- Chemical Formula
- Be3Al2Si6O18
- Composition
- Beryllium aluminum cyclosilicate. The blue color is caused by trace amounts of ferrous iron (Fe2+) substituting for aluminum in the crystal lattice.
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