Is amazonite a feldspar?
Amazonite is the blue-green variety of microcline, a potassium feldspar: hardness 6 to 6.5, density 2.54 to 2.57. How it parts from jade, turquoise and quartz.
Yes. GIA lists amazonite as the gem variety of microcline, and the International Gem Society calls it blue-green microcline, a potassium feldspar: KAlSi3O8, hardness 6 to 6.5, density 2.54 to 2.57. The IMA list has a microcline row and none for amazonite. Sold as Amazon jade, it is still feldspar: its index stops at 1.539.
In short
- The definition. GIA names two potassium feldspar species: orthoclase, with moonstone and orthoclase sunstone, and microcline, which includes the gem variety amazonite. The International Gem Society calls amazonite the blue-green variety of microcline and says it is the only microcline you are likely to encounter as a gemstone.
- The IMA test, by script. The September 2026 IMA-CNMNC Master List lists microcline as K(AlSi3O8), G, 1830, Norway. A whole-line scan finds 0 lines containing amazon. The live microcline page reaches the same conclusion; its tartan-grid test is not repeated here.
- The 1.54 line. Every index on the Handbook microcline sheet is 1.539 or below, and the gem society gives amazonite 1.522 to 1.530. Chalcedony, which includes chrysoprase, begins at 1.540 (gem society); GIA gives nephrite 1.606 to 1.632 and turquoise 1.610 to 1.650; the jadeite sheet starts at 1.640. A reading above 1.54 is not amazonite.
- Weight separates jade, not turquoise. A 20.00 g amazonite reads 12.13 to 12.22 g in water on the sheet and up to 12.40 g on the gem society’s range; GIA’s nephrite reads 13.22 g and jadeite 14.01 g. But GIA’s turquoise range, 2.40 to 2.90, reads 11.67 to 13.10 g, and the gem society’s chalcedony 12.16 to 13.13 g: both contain amazonite.
- Where the line fails, documented. Inside the feldspars the 1.54 line does nothing: oligoclase’s lowest index, 1.533, sits below microcline’s highest, 1.539, and the gem society notes the overlap between sunstone, moonstone and amazonite. It also says amazonite may be dyed, coated or impregnated, so the line identifies the host, not its treatment.
| Material | What it is (source) | Refractive index | Hardness | Density or SG; 20.00 g piece in water | Cleavage | Separated from amazonite by |
|---|---|---|---|---|---|---|
| Amazonite | Blue-green microcline, KAlSi3O8 (IGS; GIA); microcline sheet | α 1.514 to γ 1.539 (sheet); 1.522 to 1.530 (IGS) | 6 to 6.5 | 2.54 to 2.57 (sheet): 12.13 to 12.22 g; 2.54 to 2.63 (IGS): 12.13 to 12.40 g | Perfect {001} and {010}, about 90° | - |
| Chrysoprase | Translucent green chalcedony (IGS); quartz | 1.540 to 1.553 (IGS chalcedony) | 7 | 2.55 to 2.91 (IGS): 12.16 to 13.13 g; quartz sheet, massive, 2.59 to 2.63: 12.28 to 12.40 g | None useful (quartz sheet); conchoidal (IGS) | Index only by 0.001 (sheet against IGS); hardness and fracture. Not weight |
| Turquoise | CuAl6(PO4)4(OH)8(H2O)4 (IMA) | 1.610 to 1.650 (GIA) | 5 to 6 | 2.86 (sheet): 13.01 g; 2.40 to 2.90 (GIA): 11.67 to 13.10 g | None printed | Index. Not weight |
| Nephrite jade | Tremolite–actinolite rock (GIA: Ca2(Mg,Fe)5Si8O22(OH)2) | 1.606 to 1.632 (GIA) | 6.0 to 6.5 (GIA) | 2.95 (GIA): 13.22 g | Not seen in massive jade | Index and weight, at least 0.82 g |
| Jadeite jade | NaAlSi2O6 pyroxene (IMA; GIA) | α 1.640 to γ 1.692 (sheet); 1.666 to 1.680 (GIA) | 6 to 7 | 3.24 to 3.43 (sheet): 13.83 to 14.17 g; 3.34 (GIA): 14.01 g | Not seen in massive jade | Index and weight |
| “Amazon jade”, “Colorado jade” | Microcline, amazonite (Hobbs); misleading (IGS) | As amazonite | As amazonite | As amazonite | As amazonite | Nothing: it is amazonite |
| Oligoclase, for contrast | Plagioclase feldspar (sheet) | α 1.533 to γ 1.552 (sheet) | 6 to 6.5 | 2.63 to 2.66: 12.40 to 12.48 g | Perfect {001}, less perfect {010}, about 94° | Not by the 1.54 line: overlaps 1.533 to 1.539 |
Is amazonite a feldspar? What GIA, the gem society and the IMA list say
Amazonite is a feldspar: the green to blue-green variety of microcline, KAlSi3O8. GIA’s sunstone description splits the feldspar family into the potassium feldspars and the calcium-sodium plagioclases, and names two potassium species: orthoclase, which includes moonstone and orthoclase sunstone, and microcline, which includes the gem variety amazonite. The International Gem Society amazonite article says amazonite, also called Amazon stone, is the only microcline you are likely to encounter as a gemstone, and that microclines are potassium feldspars with a triclinic structure; its feldspar article calls amazonite the blue-green variety.
The IMA test, by script. The September 2026 IMA-CNMNC Master List lists microcline as K(AlSi3O8), status G, 1830, Norway. Orthoclase and sanidine share that formula on the list. A case-insensitive scan of every line finds 0 containing amazon, so there is no amazonite or amazonstone row. Amazonite is a variety name: a label reading amazonite (microcline) carries both.
What the sheet adds. The Handbook microcline sheet prints colours of white, pale cream-yellow; red, green, blue, and does not use the word amazonite. It gives hardness 6 to 6.5, density 2.54 to 2.57, perfect cleavage on {001} and {010} meeting at about 90°, and α 1.514 to γ 1.539. The species page, microcline, carries its twinning and localities; the hand-specimen method is on how to identify feldspar.
The 1.54 line: amazonite against jade, turquoise and chrysoprase
The 1.54 line: a green stone reading above 1.54 on a refractometer is not amazonite. The Handbook microcline sheet’s highest index is γ 1.539, and the International Gem Society gives amazonite 1.522 to 1.530. Every green look-alike in the table that is not a feldspar starts higher: the gem society’s chalcedony, the family that includes chrysoprase, at 1.540; GIA’s jade facts give nephrite 1.606 to 1.632 and jadeite 1.666 to 1.680; GIA’s turquoise facts 1.610 to 1.650; the jadeite sheet α 1.640.
How wide the margin is. Against jade and turquoise the gap is at least 0.067 on the printed ranges, an easy reading. Against chrysoprase it is 0.001 on the sheet, which no spot reading can resolve; there the test is hardness and fracture. Chalcedony is 7 with no cleavage, amazonite 6 to 6.5 with two perfect cleavages, and the gem society says amazonite usually shows white mottling. A scratch test is for rough only: how to test mineral hardness properly.
Jade by weight. A 20.00 g amazonite reads 12.13 to 12.22 g in water on the sheet, 12.40 g at most on the gem society’s range. GIA’s nephrite, 2.95, reads 13.22 g and its jadeite, 3.34, 14.01 g: at least 0.82 g heavier. The method is on how to measure specific gravity at home. Jade itself is on is jade a mineral; the turquoise species page is turquoise.
Where the scale fails: turquoise and chrysoprase
A documented failure: weighing cannot tell amazonite from turquoise or chrysoprase. GIA gives turquoise SG 2.76 (+0.14, −0.36), that is 2.40 to 2.90, or 11.67 to 13.10 g in water for 20.00 g, a window that contains every amazonite figure. The gem society’s chalcedony range, 2.55 to 2.91, reads 12.16 to 13.13 g, and contains them too.
Even the sheets barely part. The quartz sheet’s massive density, 2.59 to 2.63, reads 12.28 to 12.40 g; the microcline sheet’s heaviest, 2.57, reads 12.22 g. The gap is 0.06 g on a 20 g piece, and the gem society’s amazonite range, to 2.63, closes it. The chrysoprase question is on is chrysoprase chalcedony.
And inside the feldspars, the 1.54 line itself fails. The International Gem Society’s feldspar article says there is an overlap in refractive index between the low of oligoclase and the high of orthoclase and microcline, that is, between sunstone, moonstone and amazonite, and advises using appearance to verify. On the sheets the overlap is 1.533 to 1.539. The sunstone and moonstone questions are on is sunstone a feldspar and is moonstone a mineral.
When the answer changes: Amazon jade, dyed and so-called synthetic amazonite
Amazon jade is amazonite, so it is feldspar, not jade. Hobbs, Gems and Gemology, Spring 1982 lists Amazon jade and Colorado jade as misleading jade names for microcline, amazonite. The International Gem Society says vendors may market amazonite as Amazon jade, that feldspar, jadeite and nephrite are distinct, and that Amazon jade is a misleading name. The gem society’s nephrite article names amazonite among nephrite’s natural look-alikes.
Treated amazonite is still feldspar; an imitation is not. The gem society lists dyeing, wax impregnation, coating and irradiation as amazonite treatments, and says irradiation can turn white microcline blue-green, a rare but stable treatment. It also says stones sold online as synthetic amazonite may not be laboratory-grown at all, and may be look-alikes or treated natural stones. A dyed microcline passes the 1.54 line; a dyed chalcedony or glass may not. The dye checks are on how to tell if a crystal is dyed.
The radioactivity question is about potassium, not colour, and has its own page: is amazonite radioactive. This page gives no cause for amazonite’s colour; the sheet gives none either.
Why is it called amazonite? Name and localities
Named for the Amazon, not found there. The International Gem Society says amazonite has been associated with the Amazon by name since 1701 and possibly earlier, that August Breithaupt officially named it in 1847 after an unspecified type locality near the Amazon River, and that there are no known sources within the Amazon rainforest itself or near the river.
Gem localities against the sheet. The gem society names Pikes Peak, Colorado and Amelia Courthouse, Virginia for gem amazonite, and Minas Gerais in Brazil. All three are on the Handbook microcline sheet’s Distribution: the Pikes Peak area, El Paso Co., and Crystal Peak, Teller Co.; Amelia, Amelia Co., Virginia; and Minas Gerais, at Fazenda do Bananal, Salinas, Urucum and Capelinha. The sheet does not say which of its localities give green microcline, and we add no colour to them. Ethiopia and Peru, on the gem society’s list, are not on the sheet.
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