Amazonite properties are, in mineralogical terms, the properties of microcline: a potassium feldspar with the formula KAlSi₃O₈, a Mohs hardness of 6–6.5, and two perfect cleavages. What makes it amazonite is one thing only, a blue-green color that took mineralogists roughly a century to explain. This guide sticks to what can be measured.
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What Is Amazonite?
Amazonite (also called amazonstone) is the blue-green to green variety of microcline, a member of the alkali feldspar group. It is not a separate mineral species. Chemically and structurally it is the same triclinic potassium feldspar found as white, cream, or pink microcline in granites and pegmatites worldwide. Only green to blue-green microcline is called amazonite.
The name points to the Amazon River, but no significant amazonite deposits are known in the Amazon basin. The association is with the color, not the source.
Amazonite Properties at a Glance
| Mineral | Variety of microcline (potassium feldspar) |
|---|---|
| Chemical formula | KAlSi₃O₈ |
| Crystal system | Triclinic |
| Mohs hardness | 6–6.5 |
| Luster | Vitreous; pearly on cleavage surfaces |
| Cleavage | Perfect in two directions, meeting at about 90° |
| Streak | White |
| Specific gravity | 2.56–2.58 |
| Refractive index | About 1.52–1.53 |
| Color | Blue-green to green |
| Transparency | Translucent to opaque |
The hardness figure is the useful one to remember. At 6–6.5, amazonite is hard enough for cabochons and beads, but the two perfect cleavage directions mean a sharp knock can split it along those planes. That is why it is usually cut as cabochons, beads, and carvings rather than faceted, and why specimens are stored apart from harder minerals like quartz.
What Causes Amazonite's Blue-Green Color?
The color puzzled mineralogists for decades. Ordinary microcline is white, cream, or pink, and the blue-green shade has no obvious chromophore like the iron in some minerals or the copper in others. The model now widely accepted attributes it to trace lead substituting in the feldspar structure, together with water bound in the crystal lattice, with natural radiation from the surrounding rock creating the color-producing defects. Details of the mechanism are still studied, which is why color intensity varies so much between deposits and even within a single crystal.
Amazonite is not a different mineral. It is microcline that picked up the right trace elements and the right radiation history.
How to Identify Amazonite
Three features do most of the work:
- Grid pattern and white streaks. Microcline develops fine twinning that produces a cross-hatched, tartan-like grid. Amazonite also commonly carries white lamellae of albite, giving the uneven, streaky look collectors expect.
- Cleavage flash. Rotate a specimen in light and flat, pearly cleavage faces catch the light at near-right angles.
- Hardness and structure. The most common imitation is copper-bearing blue-green quartzite sold as "Guizhou jade." It is harder, has no cleavage, and shows a granular structure instead of the feldspar grid.
Where Amazonite Forms
Amazonite forms in granite pegmatites, the coarse-grained, late-stage bodies where large feldspar crystals can grow. Classic localities include Pikes Peak and Teller County in Colorado, where it occurs with smoky quartz, along with Virginia in the United States, Russia's Ural Mountains, and Madagascar. Deposits are also known in Brazil, India, Ethiopia, and Myanmar.
Frequently Asked Questions
What is amazonite's hardness on the Mohs scale?
Amazonite has a Mohs hardness of 6–6.5. It resists scratching from most everyday materials but has two perfect cleavage directions, so it can chip or split under impact.
What is the chemical formula of amazonite?
KAlSi₃O₈, potassium aluminum silicate. It is identical to the formula of microcline, because amazonite is a color variety of microcline.
Is amazonite a real mineral?
It is a variety name, not a separate species. The species is microcline, a triclinic potassium feldspar. Amazonite is the blue-green form.
What causes the blue-green color in amazonite?
Trace lead combined with water in the crystal lattice, with natural radiation creating the color-causing defects. The exact mechanism is still an active research topic.
How can you tell real amazonite from imitations?
Look for the feldspar grid pattern, white albite streaks, and flat cleavage faces with a pearly flash. Common lookalikes such as copper-bearing quartzite are harder and show no cleavage.
Wear the Science
Amazonite is a feldspar with a formula worth knowing: KAlSi₃O₈. The ISOMORPH Amazonite tee puts that chemistry on the shirt, not just the color. Shop the Amazonite tee → or browse the full Silicates collection →
Sources & Further Reading
- Handbook of Mineralogy — Microcline (data sheet)
- Geology.com — Amazonite: properties, uses, and durability
- Wikipedia — Amazonite