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Amazonite in matrix refers to specimens where the blue-green amazonite crystals are still embedded within their original host rock, typically a granitic pegmatite. The amazonite itself is a tectosilicate mineral, a variety of microcline (KAlSi3O8). Its color ranges from a pale greenish-blue to a vibrant turquoise-green, often with white streaks or inclusions of quartz or albite from the matrix. The matrix can vary in composition and texture, but commonly consists of white or grey feldspar, translucent to milky quartz, and sometimes mica flakes. The contrast between the vivid amazonite and the lighter-colored matrix can be quite striking.
How to Identify
- Color
- Varies from pale greenish-blue to intense turquoise-green. The matrix is typically white, grey, or translucent (quartz).
- Luster
- Vitreous to pearly on cleavage surfaces for amazonite; matrix minerals can be vitreous (quartz) or dull (weathered feldspar).
- Texture
- Coarse-grained, often with distinct interlocking crystals of amazonite, quartz, and other feldspars. Amazonite crystals can be anhedral to subhedral.
- Crystal Form
- Amazonite typically forms anhedral to subhedral masses or blocky crystals within the pegmatite. It belongs to the triclinic crystal system. The matrix minerals (quartz, albite) will also exhibit their characteristic crystal forms.
- Cleavage
- Amazonite (microcline) exhibits two distinct cleavages at approximately 90 degrees (89°30' to be precise), characteristic of feldspars. The matrix minerals will have their own cleavage properties (e.g., quartz has no cleavage).
- Geological Environment
- Exclusively found in granitic pegmatites, which are late-stage differentiates of granitic magmas. These pegmatites often intrude into older igneous or metamorphic rocks.
Key Facts
- Hardness: 6 to 6.5 on the Mohs scale (for amazonite and other feldspars); 7 for quartz.
- Specific Gravity: 2.56 - 2.58 g/cm³ (for amazonite).
- Crystal System: Triclinic (for amazonite/microcline).
- Color: Blue-green to turquoise-green (amazonite).
- Luster: Vitreous to pearly.
- Transparency: Translucent to opaque.
- Fracture: Uneven to conchoidal (for amazonite).
- Cleavage: Perfect in two directions at nearly 90 degrees (for amazonite).
- Composition: KAlSi3O8 (Potassium Aluminum Silicate) with trace lead for color.
Quick Check
- Color: Blue-green to turquoise-green (amazonite), with white/grey/translucent matrix.
- Luster: Vitreous to pearly (amazonite), vitreous (quartz), dull to pearly (other feldspars).
- Streak: White (for amazonite and most matrix minerals).
Physical Characteristics
- Crystal Habit: Typically anhedral to subhedral masses, blocky crystals, or tabular crystals within the pegmatite matrix.
- Cleavage Type: Perfect basal {001} and good prismatic {010} cleavage, intersecting at approximately 89°30'.
- Fracture Type: Uneven to conchoidal.
- Tenacity: Brittle.
- Luster Type: Vitreous to pearly on cleavage surfaces.
Formation
Amazonite forms as a variety of microcline, a potassium feldspar, primarily in granitic pegmatites. These pegmatites are coarse-grained igneous rocks that form from the slow crystallization of residual magma enriched in volatile components (like water, fluorine, and lithium) and incompatible elements. The distinctive blue-green color of amazonite is attributed to small amounts of lead (Pb) within the crystal lattice, replacing potassium (K), and the presence of water, which creates color centers. The 'matrix' refers to the surrounding host rock, which is typically the pegmatite itself, often composed of quartz, albite (another feldspar), muscovite, and sometimes other accessory minerals like tourmaline or garnet.
Usage
Amazonite in matrix is primarily used as an ornamental stone, for lapidary purposes (cabochons, beads, carvings), and as a collector's specimen. The presence of the matrix can enhance its aesthetic appeal, providing a natural context for the amazonite crystals. It is also used in metaphysical and spiritual practices, though these are not scientific applications.
Age Distribution
Typically associated with granitic pegmatites, which can range from Precambrian to Cenozoic, with many significant deposits being Proterozoic or Paleozoic.
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 in pegmatite pockets.
Miass, Ilmen Mountains, Russia
Historically significant locality for large, well-formed amazonite crystals.
Minas Gerais, Brazil
Produces amazonite in various shades, often in large masses within pegmatites.
Madagascar
Known for vibrant blue-green amazonite, sometimes found in large quantities.
Virginia, USA
Several pegmatite localities yield amazonite, though often not as intensely colored as Pikes Peak material.
Ethiopia
More recent discoveries have yielded good quality amazonite.
Finding Tips
Target Pegmatites
Focus your search on areas known for granitic pegmatite intrusions. These are often found in regions with ancient continental crust.
Look for Feldspar
Amazonite is a feldspar. Learn to identify common feldspars (orthoclase, albite) as they are often associated with amazonite.
Color is Key
The distinctive blue-green color is the primary identifier for amazonite. Look for this color within coarse-grained igneous rocks.
Associated Minerals
Amazonite is frequently found with quartz (often smoky quartz), albite, muscovite, and sometimes tourmaline or garnet. Identifying these associated minerals can help confirm the presence of a pegmatite environment.
Safety Precautions
When collecting in pegmatite environments, be aware of potential hazards such as unstable rock faces, sharp edges, and the presence of other minerals that might be radioactive (e.g., some uranium-bearing minerals, though not typically associated with amazonite itself, can occur in pegmatites). Always wear appropriate safety gear including gloves, eye protection, and sturdy footwear. Obtain permission before collecting on private land.
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Scientific Classification
- Mineral Class
- Tectosilicate
- Group
- Feldspar Group, Alkali Feldspar Series
- Crystal System
- Triclinic
- Chemical Formula
- KAlSi3O8 (with trace Pb for color)
- Composition
- Potassium aluminum silicate
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