Amazonite

Feldspar · also called Amazon stone, Green microcline

Amazonite is the green to blue-green variety of microcline, a potassium feldspar. Its colour comes from trace lead and structural water acted on by natural radiation, not from copper as was long believed, and because it is a colour centre it fades with heat and prolonged sunlight. White exsolution lamellae give it a distinctive grid.

What is amazonite?

Amazonite is the green to blue-green variety of microcline, a potassium feldspar. It is a rock-forming mineral that happens to take an unusual colour, and it is one of the few feldspars used decoratively for its body colour rather than for an optical effect such as adularescence or aventurescence.

Microcline is the low-temperature, triclinic form of potassium feldspar, and it almost always carries fine intergrowths of sodium feldspar exsolved during slow cooling. In amazonite these appear as the white streaks and the faint grid-like pattern that run through nearly every piece. The colour ranges from a pale mint through a strong turquoise blue-green to a deep, slightly grey green, and the best material combines even saturation with a clean white lattice rather than muddy patchiness.

It occurs almost entirely in granite pegmatites, and it is a coarse mineral: amazonite crystals of many kilograms are ordinary, and single crystals of well over a metre have been recorded. Transparent material is very rare; almost all of it is translucent to opaque, and it is worked as cabochons, beads, carvings and inlay rather than faceted.

What gives amazonite its colour?

Lead, in trace quantity, together with structural water and natural irradiation. The colour is a colour centre rather than a simple absorption by a transition-metal ion, and the mechanism was established by Hofmeister and Rossman in 1985, replacing an older explanation that attributed the green to copper.

Divalent lead substitutes for potassium in the structure at levels of a few hundred to a few thousand parts per million. Natural radiation from the surrounding granite — which is itself unusually rich in uranium, thorium and potassium in the pegmatites where amazonite forms — displaces electrons and produces the defect that absorbs in the red and yellow, leaving green and blue to be transmitted. Structural water participates, which is why dry lead-bearing microcline from other settings is not green.

This has two practical consequences. The first is that the colour is a defect rather than a stable ionic absorption, so it can be destroyed. Heating amazonite past roughly 300 degrees Celsius bleaches it, permanently in ordinary terms, and prolonged exposure to strong sunlight will fade it slowly. The second is that the colour can be restored, and returned material irradiated back to green exists in the market. Neither fact is generally disclosed at the point of sale.

How is amazonite identified?

The constants are those of microcline and they are low. Refractive index reads 1.522 to 1.530, birefringence about 0.008, specific gravity 2.55 to 2.58, hardness 6 to 6.5. Nothing else that looks like amazonite sits at a specific gravity that low.

That single number resolves most confusions. Turquoise runs 2.6 to 2.9, chrysocolla-bearing chalcedony about 2.6 to 2.8, variscite around 2.4 to 2.6 but with a refractive index near 1.56 to 1.59, and jadeite is far heavier at 3.30 to 3.38. Dyed howlite and magnesite, sold in bead form as almost anything, are softer and take a scratch far more readily.

The visual identifier is cleavage. Microcline has perfect cleavage in one direction and good cleavage in a second at close to ninety degrees, and on a cabochon this shows as flat reflective flashes that appear and disappear as the stone is rocked — quite unlike the uniform diffuse reflection of turquoise or the greasy sheen of jadeite. Combined with the white exsolution streaking, it identifies the material by eye with reasonable confidence.

The distinguishing feature: the perthitic grid

The white lattice in amazonite is not an inclusion or a vein system; it is the record of the mineral unmixing as it cooled. Potassium and sodium feldspar are miscible at high temperature and not at low, so as a pegmatite cools the sodium component separates out as fine lamellae within the potassium feldspar host. The result is called perthite, and in amazonite the white albite lamellae stand out sharply against the green.

Where microcline has also undergone the characteristic tartan twinning of the triclinic form, the pattern becomes a visible cross-hatched grid. It is diagnostic in the sense that no imitation reproduces it convincingly: dyed material shows colour concentrated along grain boundaries and around drill holes rather than a structural white lattice, and reconstituted or plastic imitations show swirl and flow rather than two intersecting directions.

The grid is also the main aesthetic variable in the material. Collectors and carvers pay for either extreme — a clean, even green with almost no streaking, or a bold, regular, high-contrast lattice. It is the muddy middle, with irregular grey-white patches, that is cheap.

Is amazonite treated?

Less often than turquoise, but the market is not clean. Three things occur.

Waxing and polymer impregnation are used on porous or fractured material to improve polish and to hold friable pieces together. This is common in low-grade beads and carvings and is rarely mentioned.

Dyeing occurs, chiefly to even out patchy colour or to push a pale piece toward a stronger blue-green. As in all dyed material, colour concentrates in fractures and around drill holes, and a cotton bud with acetone will sometimes lift traces from a dyed surface, though this test should not be performed on a stone that is not yours.

Irradiation to restore or intensify colour is technically straightforward given the mechanism, and material treated this way is present in the trade. There is no simple test to separate it, which is one of the reasons this is a stone bought on appearance rather than on a certificate.

Backing and stabilising thin slabs onto a dark substrate is also seen in inlay work and should be checked on any piece where the edge of the stone is hidden by the setting.

Where does amazonite come from?

Colorado is the classic source. The granite pegmatites of the Pikes Peak batholith, particularly around Crystal Peak in Teller County, produce the blue-green crystals in association with smoky quartz that are among the most recognisable mineral specimens from North America. Amelia Court House in Virginia is the other historic American locality.

Russia has produced amazonite for centuries from the Ilmen Mountains in the southern Urals and from the Kola Peninsula, where the Ploskaya Mountain occurrences yield large masses of strong colour. Russian material supplied the imperial lapidary works and appears in nineteenth-century Russian decorative stonework.

Madagascar and Brazil are the main current sources of bulk commercial material for beads and carvings, and Madagascan amazonite in particular dominates the low-cost end of the market. Smaller quantities come from a number of pegmatite districts worldwide; the mineral is not rare, and the constraint is even colour rather than supply.

Where the name comes from

The name refers to the Amazon River and is almost certainly a mistake. No amazonite deposit of consequence has ever been found in the Amazon basin, and the green stones reported from that region by early European accounts — the material that gave rise to the name in the eighteenth century — were most probably nephrite or another green material entirely.

The mineral itself has a far longer human history than the name. Amazonite beads and inlay appear in ancient Egyptian work, including pieces from the tomb of Tutankhamun, and in Mesopotamian objects; some of the Egyptian material is thought to have come from the Eastern Desert. It is one of a small group of green and blue stones — with turquoise, malachite and faience — that carried a consistent decorative importance across the ancient Near East.

What sizes are available?

Effectively unlimited for anything opaque. Amazonite forms in metre-scale pegmatite crystals and is quarried in blocks, so bowls, spheres, book-matched slabs, large carvings and architectural inlay are all straightforward. Nothing in the material argues against size.

Transparent to semi-transparent material is the exception. It is genuinely rare, is faceted only occasionally, and is a collector's curiosity rather than a jewellery stone — partly because the perfect cleavage makes faceting and setting awkward, and partly because a transparent pale green feldspar has no commercial constituency.

What is scarce at size is even colour. Large pieces almost always show variation in saturation and in the density of white streaking, so a carving of any size that holds one consistent green across its whole surface is worth substantially more per unit than the same weight of variable material.

How much is amazonite worth?

It is an inexpensive material, and price is set almost entirely by appearance rather than by weight, origin or certification.

Evenness and depth of colour lead. A saturated blue-green that holds across the whole piece, without grey or brown zoning, sits at the top. Pattern comes next, and the market rewards the two extremes — a clean minimal lattice or a bold, regular, high-contrast grid — over irregular patchiness. Then translucency, then the quality of the polish, which matters because a feldspar with two cleavage directions is genuinely difficult to finish well and a poorly polished surface will show cleavage pits.

Fine crystallised specimens from Pikes Peak, especially the classic combinations of amazonite crystals with smoky quartz, trade in the mineral specimen market at prices unrelated to the value of the same material as a lapidary stone. Anyone comparing prices should be clear which of the two markets they are in.

Is amazonite durable enough to wear?

With care. At 6 to 6.5 on the Mohs scale amazonite is softer than airborne dust, which contains quartz at hardness 7, so a polished surface in daily wear will dull over time. The more serious issue is cleavage: perfect in one direction and good in a second, meeting at close to a right angle, which means a sharp knock can part the stone cleanly rather than merely chipping it.

That combination makes it a good material for earrings, pendants, brooches and beads, and a poor one for a ring worn daily. In a ring it should be set in a bezel that protects the edges, and the wearer should expect to have it repolished eventually.

Care is simple but strict. Warm water, mild soap and a soft cloth only. No ultrasonic cleaner, because cleavage and any wax or polymer treatment will both suffer. No steam. No prolonged direct sunlight, since the colour centre fades. And keep it away from heat entirely — a piece left on a windowsill or subjected to a jeweller's torch can lose its colour outright and will not recover it.

How to buy amazonite without being caught out

Look for the white lattice. It is the single most reliable sign that you are holding feldspar rather than dyed howlite, reconstituted composite or plastic, and it cannot be faked convincingly. Rock the stone under a light and look for the flat cleavage flashes as well.

Check the drill holes on beads. Dye pools there and in fractures, and a bead strand is the easiest place in the whole trade to see whether colour is structural or applied.

Ask about wax and polymer, particularly on carvings and on anything with a suspiciously perfect polish over visible fractures. And ask where the piece has been kept, because a faded amazonite is a permanent condition unless it is re-irradiated, and a strong even colour in an old piece is a better sign than a strong even colour in a new one.

Then buy it on the eye. This is not a stone that rewards certification, and no report will tell you what the piece looks like. Browse our specimens, our gems, or tell us what you are looking for.

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