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Amazonite is a tectosilicate mineral, a variety of microcline feldspar, known for its distinctive blue-green to green color. The color is attributed to small amounts of lead (Pb) within the crystal lattice, replacing potassium (K), and the presence of water, rather than copper as was once believed. It typically forms in well-formed crystals within pegmatite pockets or as massive aggregates.
How to Identify
- Color
- Characteristic blue-green to green, sometimes with white streaks or inclusions. The color can vary in intensity.
- Luster
- Vitreous (glassy) to pearly on cleavage surfaces.
- Texture
- Typically massive or in well-formed, often tabular, crystals. Can exhibit a fine lamellar twinning (perthitic texture) visible on polished surfaces.
- Crystal Form
- Usually forms in anhedral to subhedral masses, but can also occur as distinct, often blocky or tabular, triclinic crystals. Twinning, particularly polysynthetic twinning (albite twinning) and pericline twinning, is common and can be observed as fine striations on cleavage surfaces.
- Cleavage
- Perfect cleavage in two directions, nearly at right angles (approximately 90 degrees, specifically 90° 30'). This is characteristic of feldspar minerals.
- Geological Environment
- Primarily found in granitic pegmatites, which are igneous intrusions characterized by very large crystals. Less commonly found in granites and some metamorphic rocks.
Key Facts
- Hardness: 6 to 6.5 on the Mohs scale
- Specific Gravity: 2.56 to 2.58
- Crystal System: Triclinic
- Color: Blue-green, green, sometimes with white streaks
- Luster: Vitreous to pearly
- Transparency: Translucent to opaque
- Fracture: Uneven to conchoidal
- Cleavage: Perfect in two directions, nearly at 90 degrees (90° 30')
- Composition: Potassium aluminum silicate (KAlSi3O8)
Quick Check
- Color: Blue-green to green
- Luster: Vitreous to pearly
- Streak: White
Physical Characteristics
- Crystal Habit: Massive, granular, or in well-formed tabular to blocky crystals, often twinned.
- Cleavage Type: Perfect basal {001} and good prismatic {010}, intersecting at approximately 90° 30'.
- Fracture Type: Uneven to conchoidal.
- Tenacity: Brittle.
- Luster Type: Vitreous on crystal faces, pearly on cleavage surfaces.
Formation
Amazonite forms in granitic pegmatites, which are coarse-grained igneous rocks that crystallize from residual magma enriched in volatile components and incompatible elements. It can also occur in some granites and metamorphic rocks.
Usage
Primarily used as a gemstone and ornamental stone due to its attractive blue-green color. It is carved into cabochons, beads, and small sculptures. Historically, it has been used for decorative purposes and in jewelry.
Age Distribution
Found in various geological ages, primarily associated with granitic pegmatites which can range from Precambrian to Cenozoic.
Where to Find
Pikes Peak, Colorado, USA
Famous for producing some of the finest deep blue-green amazonite crystals, often associated with smoky quartz and albite.
Miass, Ilmen Mountains, Russia
Historically significant locality, known for large amazonite crystals.
Minas Gerais, Brazil
A major source of amazonite, often found in pegmatites.
Madagascar
Produces good quality amazonite, sometimes with interesting patterns.
Virginia, USA
Localities such as Amelia Courthouse are known for amazonite occurrences.
Ethiopia
Newer sources have emerged, providing material for the gem market.
Finding Tips
Target Pegmatites
Focus your search on granitic pegmatite dikes and sills, especially those known for rare earth elements or other unusual minerals, as amazonite often co-occurs with them.
Look for Associated Minerals
Amazonite is frequently found with smoky quartz, albite, cleavelandite, and sometimes other rare minerals like topaz or beryl. Identifying these associated minerals can lead to amazonite.
Examine Outcrops
Look for distinctive blue-green masses or crystals within exposed pegmatite bodies. Weathering can sometimes make the color more apparent.
Check Mine Dumps
Old mine dumps from pegmatite operations can be excellent places to find specimens that were overlooked or discarded.
Similar Rocks
Turquoise
CuAl6(PO4)4(OH)8·4H2O
Also known as: Callais
Chrysocolla
(Cu,Al)2H2Si2O5(OH)4·nH2O
Also known as: Gem Silica
Jade (Nephrite or Jadeite)
Ca2(Mg,Fe)5Si8O22(OH)2 (Nephrite); Na(Al,Fe3+)Si2O6 (Jadeite)
Also known as: Stone of Heaven
Scientific Classification
- Mineral Class
- Tectosilicate
- Group
- Feldspar Group, Alkali Feldspar Series
- Crystal System
- Triclinic
- Chemical Formula
- KAlSi3O8
- Composition
- Potassium aluminum silicate. The blue-green color is due to trace amounts of lead (Pb) and water within the crystal structure.
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