Amazonite: Why This Feldspar Turns Blue-Green

Short answer: amazonite is the blue-green variety of microcline, a potassium feldspar (KAlSi3O8). Its color comes from trace lead that has been altered by natural radiation, with water in the crystal also required. It is hard enough to polish (Mohs 6 to 6.5) but splits easily along two cleavages at about 90 degrees. The classic crystals come from the Pikes Peak area of Colorado, often paired with smoky quartz.

Where does amazonite's color come from?

This is the question most guides skip, and the answer is more interesting than "copper," which is what amazonite was assumed to contain for a long time. The Caltech Mineral Spectroscopy server, maintained by George Rossman's lab, explains that blue color in amazonite comes from the interaction of trace amounts of Pb2+ in the feldspar with ionizing radiation, usually from the decay of potassium-40 in the feldspar itself. Water molecules must also be present in the structure for the coloration to occur.

So three ingredients have to meet: a little lead, a little water, and a long dose of low-level radiation from the crystal's own potassium. The amounts are tiny. Caltech's reference samples include a sky blue Brazilian microcline with about 300 ppm lead, a turbid blue perthite from Lake George, Colorado with about 700 ppm, and a coarse green perthite from Pearl, Colorado with 0.8 wt% PbO.

The same page explains why some pieces read blue and others green. Lead-bearing feldspars with more disordered aluminum and silicon (typically orthoclase) are green, while the more ordered microcline becomes blue under irradiation; partly ordered feldspars show both. That is the chemistry behind the trade's range from sky blue to minty green.

Because the color is a radiation-induced effect, heat can undo it. In a Caltech experiment on lead-bearing blue albite from Kenya, heating to 300 °C for 25 minutes removed much of the color, and gamma irradiation brought it back stronger. Treat that as a warning for amazonite too: keep it away from torches, kilns and jewelry repair heat.

What is amazonite, mineralogically?

Amazonite is microcline, one of three potassium feldspars with the same formula. Minerals.net explains that microcline, orthoclase and sanidine are almost identical in physical properties and often impossible to separate without X-ray analysis, the only difference being crystal structure: microcline is triclinic, the other two monoclinic. A deep green color, it adds, is a tell-tale sign of microcline, since orthoclase does not occur in that color. Webmineral traces the name to the Greek mikron, "little," and klinein, "to stoop," a reference to cleavages that meet just slightly off a right angle, and lists "Amazonstone" as its synonym for green microcline. Geology.com's feldspar page places amazonite among the popular feldspar gems alongside moonstone, sunstone, labradorite and spectrolite. The wider family is covered in the feldspar guide.

Those numbers come from the Minerals.net amazonite page and Geology.com, which adds the diagnostic combination worth remembering: green to bluish green color, two cleavages meeting near 90 degrees, and a pearly sheen on some cleavage faces.

Why does amazonite have white streaks and a grid pattern?

Look closely at almost any polished amazonite and you will see two kinds of pattern.

• White streaks and patches. These are usually albite, a sodium feldspar that separated out of the potassium feldspar as it cooled. Minerals.net notes that microcline intergrown with albite in alternating patterns forms a feldspar rock known as perthite. Geology.com adds that the color is often interrupted by streaks of white quartz or feldspar.
• A fine cross-hatched grid. Geology.com shows cabochons with an interesting cross-hatched pattern. In microcline this tartan-like texture comes from twinning in two directions, and it is one of the best visual signs that a green stone is feldspar rather than jade or glass.

Neither pattern is a defect. Even, saturated color with little white is rarer and priced higher, but a lively perthite pattern is part of amazonite's character.

Where are the best amazonite crystals found?

Amazonite grows in granite pegmatites, where large feldspar crystals have room to form in open pockets. The pegmatite guide explains how those pockets develop.

Colorado is the benchmark. Minerals.net calls some of the finest material the Pikes Peak area, which spans El Paso, Teller, Douglas and Park counties, with exceptional deposits at Pikes Peak, Crystal Peak, Devils Head, Lake George and Florissant; all of it may be called "Pikes Peak amazonite." Geology.com pictures a blue cluster from the Jack Rabbit Mine in Teller County measuring 8.5 by 7.0 by 5.5 centimeters and notes that Teller County amazonite is often accompanied by large prismatic crystals of smoky quartz. That blue-green and smoky brown pairing is one of the best known combinations in American mineral collecting.

Common companions, per Geology.com, include albite, cleavelandite, quartz and schorl tourmaline. Most tumbled and carved amazonite comes from massive pegmatite rock rather than from crystal pockets, which is why polished pieces are inexpensive while sharp Colorado crystals are not.

Why is it called amazonite?

Geology.com notes the gem was first called "Amazon stone" after the Amazon River, although there are no known occurrences near that river, and that it has been used as a gem for over 2,000 years, turning up in archaeological excavations in ancient Egypt and Mesopotamia. It also flags "Amazon jade" as a misnomer, a name that implies a more valuable identity, and notes that sellers using misnomers can face action from the Federal Trade Commission.

How do you tell amazonite from jade, larimar and other look-alikes?

Treatment is rarely a concern. Minerals.net states that amazonite gemstones are not treated or enhanced, which matches the trade: the material is plentiful and cheap enough that treating it does not pay.

How durable is amazonite, and how should you care for it?

Geology.com names two durability issues: the 6 to 6.5 hardness, which lets it be scratched in everyday wear, and the two directions of perfect cleavage, along which it breaks if knocked. It recommends earrings, pendants and pins over rings and bracelets, and protective bezel settings for cabochons. For carvings and palm stones the same advice applies: a drop onto tile can split a piece cleanly along a cleavage plane.

Clean amazonite with lukewarm water and a soft cloth, and dry it. Avoid ultrasonic cleaners, which can open cleavage cracks, and avoid heat, which can fade the color as described above.

Amazonite in crystal traditions

In crystal traditions amazonite is associated with courage, honest communication and calm. These are cultural associations rather than measurable properties.

Choosing amazonite: what to look for

For polished pieces, judge saturation (blue-green and vivid beats pale and grayish), how much white perthite you like, and whether there are cleavage cracks that catch the light like internal mirrors. For crystals, look for sharp faces, a named locality and companions such as smoky quartz. Ask for dimensions; feldspar is light enough that a palm stone and a tower of similar weight can differ a lot in size.

Examples currently in stock:

• Amazonite freeforms and towers: polished freeforms around 2.5 to 2.75 inches and towers up to 6 inches tall, large enough to see the white perthite streaks and the color range across one piece.
• Amazonite palm stones and tumbles: palm stones of about 2.25 to 2.5 inches and small tumbles, the cheapest way to study the grid and streak pattern under a loupe.
• Larimar: tumbles, medium pieces and spheres of the stone most often confused with pale amazonite, useful for a side by side comparison.
• Smoky quartz: the classic pegmatite companion of Colorado amazonite; pairing the two shows why collectors prize the combination.
• Sunstone sphere: a 74 mm sphere of another feldspar, a reminder that the same mineral family produces glittering orange as well as blue-green.

Frequently asked questions

What gives amazonite its blue-green color?

Trace lead in the microcline, altered by natural radiation from the decay of potassium in the feldspar, with water molecules present in the structure. More ordered microcline turns blue and more disordered feldspar turns green. The color is a radiation effect, so strong heat can fade it.

Is amazonite a type of jade?

No. Amazonite is microcline feldspar, while jade is nephrite or jadeite. "Amazon jade" is a misleading trade name. Amazonite usually shows white streaks of albite, a cross-hatched grid and flat cleavage flashes, none of which jade has.

Is amazonite durable enough for a ring?

It is risky. Amazonite rates 6 to 6.5 on the Mohs scale and has two perfect cleavages, so a hard knock can split it. Pendants, earrings and pins are safer, and a protective bezel setting helps if you do want a ring.

Where does the best amazonite come from?

The Pikes Peak area of Colorado is the classic source of crystal specimens, often with smoky quartz. Deep green amazonite also comes from the Kola Peninsula in Russia, Minas Gerais in Brazil, Ethiopia and Myanmar. Polished amazonite usually comes from massive pegmatite rock rather than crystal pockets.

Can amazonite go in water?

A quick rinse is fine, since amazonite does not dissolve. Avoid long soaks and ultrasonic cleaners, which can work into cleavage cracks, and dry it after cleaning. Keep it away from heat, which can fade the color.

Sources

• Caltech Mineral Spectroscopy Server, Feldspar spectra: http://minerals.gps.caltech.edu/files/visible/feldspar/index.html
• Minerals.net, Microcline: https://www.minerals.net/mineral/microcline.aspx
• Minerals.net, Amazonite gemstone: https://www.minerals.net/gemstone/amazonite_gemstone.aspx
• Geology.com, Amazonite: https://geology.com/gemstones/amazonite/
• Webmineral, Microcline Mineral Data: https://www.webmineral.com/data/Microcline.shtml
• Geology.com, Feldspar: https://geology.com/minerals/feldspar.shtml