Authenticating Amazonite: Formation, Testing & Quality

January 26, 2025 Candice Hamilton

Geography & Geological Formation

Amazonite belongs to the feldspar mineral family which is a type of silicate mineral (along with quartz, mica and olivine). Silicate minerals make up about 90% of the Earth's crust which makes them the most abundant group of minerals in the Earth's crust. Feldspars are divided into two main groups: potassium feldspars (orthoclase, microcline, and sanidine) and plagioclase feldspars (albite to anorthite series).

Amazonite is a variety of microcline, which is a potassium feldspar. Amazonite forms in granitic rocks, particularly in pegmatites, which are very coarse-grained igneous rocks. Pegmatites provide the slow cooling necessary for the growth of large crystals. Amazonite often forms in association with minerals like smoky quartz, orthoclase, and albite.

The geological conditions required for its formation include high temperatures and the presence of volatile components like water. Amazonite is found in various parts of the world. Significant deposits include:

Russia: Historically sourced from the Ilmensky Mountains (Southern Urals) near Chelyabinsk.

United States: Notable sites in Colorado (Pikes Peak, Crystal Peak) and Virginia.

Brazil: Known for high-quality specimens.

Madagascar, Ethiopia, and China are other prominent sources of amazonite.

Feldspar Family

Diagram showing the breakdown of feldspar varieities.

Chemical Composition & Colouring

The chemical formula of amazonite is K(AlSi₃O₈), indicating it is composed of potassium (K), aluminium (Al), silicon (Si), and oxygen (O).

Amazonite gets its colour primarily from the presence of trace amounts of lead (Pb) and water within its crystal structure.

When lead is present in the feldspar, it can substitute for potassium (K) in the crystal lattice. This substitution causes distortion in the crystal lattice, which affects how light interacts with the mineral, leading to the green colour we see.

The exact shade can vary based on the concentration and distribution of lead and other trace elements like rubidium and thallium. This colouration process was first detailed in a 1985 study by Hoffmeister and Rossman.

Additionally, some studies suggest that the colour can also be influenced by the presence of iron (Fe) impurities and radiation exposure over time. These factors can create defects and colour centres within the crystal, further contributing to the unique green hue of amazonite.

Fig 1. Fig 1. The atoms present in the crystal lattice. The potassium (K) is loosely bonded with aluminium (Al), silicon (Si) and oxygen (O).

Fig 2. When a tiny number of potassium (K) atoms are replaced by lead (Pb) in the lattice, with the presence of a hydroxyl (OH) group (that creates the water), we get the green colour typical of amazonite.

Note: The crystal lattice structures are loose representations for illustrative purposes only due to complexity of demonstrating 3D shapes in 2D.

Identification Of Amazonite

SUGGESTED TESTING METHODS
We recommend using the following standard gemmological tools and methods to determine authenticity:

Chelsea Filter

Conoscope

Dichroscope

Loupe

Polariscope

Refractometer

Specific Gravity

Spectroscope

Ultraviolet (UV) Light

OBSERVATION
Amazonite is always a green to blue-green colour. The hue can range from pale to intense, often with a slightly mottled appearance due to its natural mineral composition. It has a vitreous (glass-like) lustre on its polished surfaces. Look for the characteristic grid-like pattern of white streaks or lines, which is a result of the mineral's cleavage planes. Amazonite is usually opaque, though it can sometimes be slightly translucent around the edges if held up to a strong light source.

Close-up: Granular texture

LOUPE (OR MICROSCOPE)
Examine the cleavage planes more closely. Amazonite often shows two directions of perfect cleavage at nearly right angles, which can be seen as parallel lines or steps on broken surfaces. Look for the texture of the surface.

Natural amazonite will have a slightly uneven, sometimes granular texture, especially in unpolished areas. The grid-like pattern of white streaks becomes more evident. These are typically aligned along the cleavage planes and can help confirm the identity of the stone.

Close-up: Granular texture showing cleavage planes.

Close-up: white albite streaks

SPECIFIC GRAVITY
Specific gravity (SG), also called relative density, is a measure of the density of a mineral compared to the density of water. The calculated specific gravity for amazonite should fall within the range of 2.56 to 2.58. If the value falls within this range, it supports the identification of the stone as amazonite. A significant deviation might indicate a different material. This can be measured using a hydrostatic balance.

Amazonite Gallery

similar materials, misnomers & synonyms

SIMILAR MATERIALS

Turquoise: Amazonite can sometimes be mistaken for turquoise due to their similar blue-green colour, but turquoise typically has a more distinct veined pattern.
Chrysocolla: Both stones can exhibit blue-green hues, but chrysocolla often has a more mixed and mottled appearance.

SYNONYMS

Amazon Stone: A common old term for amazonite, stemming from the belief that it was once found in the Amazon River region, though this is not true.
Microcline Feldspar: Amazonite is a variety of microcline, a potassium feldspar, so this term is sometimes used interchangeably, especially in scientific contexts.

MISNOMERS

Amazon Jade: Sometimes used incorrectly to refer to amazonite as it is not a jade. Jade is used to created a perceived higher value.

Enhancements & Artificial Materials

TREATMENTS
Amazonite is generally not subjected to treatments to enhance its colour or clarity. Unlike some other gemstones that are often heat-treated, dyed, or otherwise altered to improve their appearance, amazonite's vibrant green to bluish-green hues are natural. This lack of treatment maintains the stone's natural beauty and appeal.

There has, however, been an increase in impregnated amazonite in the market - particularly beaded bracelets. An article published by the GIA (Gems & Gemology, Fall 2017, Vol. 53, No. 3) discusses the appearance of high-quality, translucent blue amazonite in the jewellery market. Analysis revealed the stone's vivid blue colour is enhanced by resin impregnation, which completely penetrates the material.

SYNTHETIC
As of now, there are no known synthetic versions of amazonite being produced for the market. The unique combination of its colour and mineral properties has not been replicated in a laboratory setting. However, it is always important to purchase gemstones from reputable dealers to ensure authenticity, as the market can sometimes see imitations or mislabeled stones.

Image: Natural amazonite beads.

Image: Impregnated amazonite beads sold on Etsy as ‘natural’.

Amazonite buying guide

HIGHER QUALITY

Lustre: Bright, vitreous, and smooth, reflecting light well.

Colour: Rich, vibrant blue-green or green with consistent saturation throughout.

Mottling Even, fine mottling or grid-like pattern that enhances the stone's visual appeal.

Condition: Shows no signs of surface scratches or wear, indicating proper handling and care.

Matrix: Complementary host rock (if present), with well-integrated amazonite that is firmly attached.

LOWER QUALITY

Lustre: Dull or lacklustre, with poor surface polish that diminishes light reflection.

Colour: Faded, pale, or washed-out blue-green hues with uneven colour distribution or discolouration. Dominant white streaks that reduce visual quality.

Mottling: Poorly formed or distorted crystals. Rounded edges and rough faces.

Condition: Chips, cracks, or surface scratches; large, visible inclusions that affect the overall appearance.

Matrix: Excessive or unattractive host rock that overwhelms the Amazonite, with poorly adhered or loose crystals.

Higher quality

Lower quality

The Spiritual Gemmologist