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Amazonite is a striking blue-green to green variety of microcline, a potassium feldspar. It is known for its vibrant color, which can range from pale greenish-blue to an intense turquoise. It often exhibits a characteristic white streaking or mottling due to perthitic exsolution lamellae of albite. Its name is derived from the Amazon River, although it is not found there; the name likely arose from confusion with another green mineral found in the region.
How to Identify
- Color
- Typically blue-green to green, sometimes with white streaks or mottling.
- Luster
- Vitreous (glassy) to pearly on cleavage surfaces.
- Texture
- Often exhibits a granular or massive texture, but can also form well-developed prismatic crystals.
- Crystal Form
- Usually occurs as anhedral to subhedral masses, or as well-formed triclinic crystals, often twinned (e.g., Carlsbad, Baveno, Manebach twins).
- Cleavage
- Perfect cleavage in two directions, nearly at right angles (approximately 90 degrees).
- Geological Environment
- Primarily found in granitic pegmatites, but also in some hydrothermal veins and 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
- Composition: Potassium aluminum silicate (KAlSi3O8)
Quick Check
- Color: Blue-green to green
- Luster: Vitreous to pearly
- Streak: White
Physical Characteristics
- Crystal Habit: Prismatic, tabular, massive, granular
- Cleavage Type: Perfect on {001} and {010}, nearly at 90 degrees
- Fracture Type: Uneven to conchoidal
- Tenacity: Brittle
- Luster Type: Vitreous to pearly
Formation
Amazonite is a tectosilicate mineral, a variety of microcline, which is a potassium-rich feldspar. Its distinctive blue-green color is attributed to small amounts of lead (Pb) and water (H2O) within its crystal lattice, rather than copper as was once believed. It 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 be found in some metamorphic rocks and hydrothermal veins.
Usage
Primarily used as a gemstone and ornamental stone due to its attractive blue-green color. It is often cut into cabochons, beads, and carved into various decorative objects. It is also collected by mineral enthusiasts.
Age Distribution
Found in various geological ages, typically associated with late-stage magmatic and hydrothermal processes.
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 for amazonite, producing large crystals.
Minas Gerais, Brazil
Known for producing good quality amazonite, often found in pegmatites.
Madagascar
A significant source of amazonite, often found in large masses suitable for carving.
Virginia, USA
Localities such as Amelia Courthouse have produced amazonite.
Ethiopia
Emerging source of amazonite, often with attractive color.
Finding Tips
Target Pegmatites
Focus your search on granitic pegmatite dikes, especially those known for producing other rare minerals. Look for areas with exposed bedrock or old mine dumps.
Look for Associated Minerals
Amazonite often occurs with smoky quartz, albite, cleavelandite, and sometimes topaz or beryl. The presence of these minerals can indicate a favorable environment.
Examine Color and Luster
Its distinctive blue-green color and vitreous to pearly luster are key identifiers. Look for areas where the rock has a distinct greenish-blue hue.
Check for Cleavage
If you find a piece, observe its cleavage planes. Amazonite (microcline) exhibits two perfect cleavages at nearly 90 degrees.
Safety Precautions
When collecting in pegmatite environments, be aware of unstable rock, old mine workings, and potential for sharp edges. Always wear appropriate safety gear including gloves and eye protection.
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/Jadeite)
Ca2(Mg,Fe)5Si8O22(OH)2 (Nephrite) / Na(Al,Fe3+)Si2O6 (Jadeite)
Also known as: Greenstone
Scientific Classification
- Mineral Class
- Tectosilicate
- Group
- Feldspar Group, Alkali Feldspar Series
- Crystal System
- Triclinic
- Chemical Formula
- KAlSi3O8
- Composition
- Potassium aluminum silicate
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