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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 characteristic color. The color is caused by trace amounts of ferrous iron (Fe2+) within the beryl crystal structure. It typically forms as hexagonal prisms, often with striations parallel to the c-axis. It is known for its excellent clarity and vitreous luster.
How to Identify
- Color
- Ranges from pale blue to deep blue-green. The color is typically uniform, but some crystals may exhibit slight pleochroism (appearing different colors when viewed from different angles).
- Luster
- Vitreous (glassy).
- Texture
- Smooth to the touch, due to its hardness and lack of prominent cleavage.
- Crystal Form
- Hexagonal prisms, often elongated, with flat basal terminations. Striations parallel to the c-axis are common.
- Cleavage
- Imperfect basal cleavage, meaning it tends to break along flat planes perpendicular to the long axis, but not easily or cleanly.
- Geological Environment
- Granitic pegmatites, hydrothermal veins, and sometimes in metamorphic rocks. Often associated with minerals like quartz, feldspar, muscovite, and sometimes tourmaline or garnet.
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) with trace iron (Fe2+)
Quick Check
- Color: Pale blue to deep blue-green
- Luster: Vitreous (glassy)
- Streak: White
Physical Characteristics
- Crystal Habit: Prismatic, typically hexagonal, often elongated and striated parallel to the c-axis. Can also be massive.
- Cleavage Type: Imperfect basal {0001}. While present, it is not easily observed and does not typically affect durability in jewelry.
- Fracture Type: Conchoidal to uneven. Breaks with smooth, curved surfaces (conchoidal) or irregular, rough surfaces (uneven).
- Tenacity: Brittle. It can break or chip if subjected to sharp impact.
- Luster Type: Vitreous (glassy).
Formation
Aquamarine forms in the late stages of magmatic crystallization, primarily in granitic pegmatites, which are coarse-grained igneous rocks. It can also be found in hydrothermal veins and sometimes in metamorphic rocks. The presence of beryllium, aluminum, and silicon, along with trace amounts of iron (Fe2+), is crucial for its formation and characteristic blue-green color. The slow cooling of these pegmatitic melts allows for the growth of large, well-formed crystals.
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. Historically, it was also used for optical lenses due to its clarity, though this is less common today.
Age Distribution
Aquamarine forms in pegmatites and hydrothermal veins, which can range in age from Precambrian to Cenozoic, depending on the specific geological event.
Where to Find
Minas Gerais, Brazil
One of the most significant sources, producing large, high-quality crystals, including the famous 'Dom Pedro' aquamarine.
Pakistan
Known for producing fine, often intensely colored aquamarine crystals, particularly from the Shigar Valley and Gilgit-Baltistan regions.
Nigeria
Emerging as a significant source, producing good quality blue aquamarine.
Madagascar
Produces a range of aquamarine qualities, often with a slightly greenish-blue hue.
Russia (Ural Mountains)
Historically important source, particularly for older specimens.
United States (Colorado, California)
Smaller deposits, but some notable finds have occurred, particularly in the Mount Antero region of Colorado.
Finding Tips
Look in Pegmatite Dikes
Focus your search in areas known for granitic pegmatites, especially those with coarse-grained textures. Look for exposed dikes or weathered material derived from them.
Identify Associated Minerals
Aquamarine is often found alongside quartz, feldspar (orthoclase, albite), muscovite, and sometimes tourmaline or garnet. The presence of these minerals can indicate a favorable environment.
Check for Hexagonal Prisms
Keep an eye out for characteristic hexagonal crystal forms, which can be indicative of beryl. Even small fragments might show this habit.
Examine Color and Luster
Look for transparent to translucent blue to blue-green crystals with a vitreous luster. The color can vary in intensity.
Safety Precautions
Beryl contains beryllium, which can be toxic if inhaled as fine dust. While handling solid aquamarine is generally safe, avoid grinding or cutting without proper ventilation and respiratory protection. Always wear appropriate personal protective equipment (PPE) when prospecting, including eye protection and gloves.
Similar Rocks
Topaz
Al2SiO4(F,OH)2
Also known as: Imperial Topaz, Blue Topaz
Blue Zircon
ZrSiO4
Also known as: Starlight Zircon
Euclase
BeAlSiO4(OH)
Also known as: None
Blue Tourmaline
Complex borosilicate
Also known as: Indicolite
Scientific Classification
- Mineral Class
- Silicates
- Group
- Cyclosilicates (Beryl Group)
- Crystal System
- Hexagonal
- Chemical Formula
- Be3Al2Si6O18
- Composition
- Beryllium aluminum cyclosilicate. The blue color is due to trace amounts of ferrous iron (Fe2+) substituting for aluminum in the crystal lattice. Heating can sometimes enhance the blue color by altering the oxidation state of iron.
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