Is sunstone a feldspar?
Sunstone is feldspar with a copper or hematite glitter: orthoclase, oligoclase or labradorite, hardness 6 to 7.2 (GIA). Where a sunstone label is not feldspar.
Yes. GIA calls sunstone a member of the feldspar group: orthoclase, oligoclase or labradorite showing aventurescence, a glitter from flat reflective inclusions. On GIA’s figures the three read 1.518 to 1.526, 1.537 to 1.547 and 1.559 to 1.568 on a refractometer. Goldstone glass and aventurine quartz glitter too, but are not feldspar.
In short
- The definition. GIA says both the orthoclase and the plagioclase feldspars have a sunstone variety, that the name refers to the gem’s appearance rather than its chemical makeup, and that gemmologists call it aventurine feldspar when aventurescence is present. GIA’s Gems and Gemology review of phenomenal gems (Summer 2025) says gem-quality aventurine feldspars are typically known as sunstones.
- Not a species name. A case-insensitive scan of every line of the September 2026 IMA-CNMNC Master List finds 0 containing sunstone, oligoclase or labradorite; orthoclase and albite have rows. A script over the 10 Handbook feldspar sheets finds none printing sunstone, aventur- or hematite. The name lives in gemmology, not in the species lists.
- The three-band rule. GIA’s sunstone facts give orthoclase sunstone 1.518 to 1.526, oligoclase sunstone 1.537 to 1.547 and labradorite sunstone 1.559 to 1.568, with gaps of 0.011 and 0.012 between them. A refractometer reading in a band names the feldspar; at GIA’s specific gravities a 20.00 g piece reads 12.25, 12.45 and 12.59 g in water.
- Where the rule fails. Andesine, at 1.543 to 1.551 in the International Gem Society’s table, overlaps the oligoclase band; GIA says Tibetan andesine sold as sunstone may have been pale Mongolian andesine infused with copper. Oligoclase sunstone at 2.65 weighs the same as quartz, and orthoclase sunstone shares GIA’s moonstone figures, 1.518 to 1.526 and 2.58, exactly.
- The boundary. GIA’s 2025 review traces the word aventurine to a glittering glass now called goldstone, says it was first used in mineralogy for quartzite with mica, and calls the aventurescence of gold sheen sapphire comparable to sunstone’s. Glitter alone does not make a feldspar; the aventurine question is on is aventurine a quartz.
| Label or material | What the source says it is | Refractive index | SG; 20.00 g piece in water | Reflector (source) | A feldspar? |
|---|---|---|---|---|---|
| Orthoclase sunstone | Potassium feldspar (GIA); Tanzania and Australia examples (GIA 2025) | 1.518 to 1.526 (GIA) | 2.58; 12.25 g | Long hematite blades (GIA 2025) | Yes |
| Oligoclase sunstone | Sodic plagioclase; Tvedestrand the most studied (GIA 2025) | 1.537 to 1.547 (GIA) | 2.65; 12.45 g | Hematite plates (GIA 2025); hematite or goethite (IGS) | Yes |
| Labradorite sunstone, Oregon | Labradorite in basalt (GIA 2025); most Oregon sunstones are labradorites (GIA 2025) | 1.559 to 1.568 (GIA) | 2.70; 12.59 g | Copper platelets, mostly along (010) (GIA 2025) | Yes |
| Oregon sunstone without glitter | Gem basaltic feldspar sold as Oregon sunstone though not all show aventurescence (GIA 2025) | As labradorite | As labradorite | None | Yes, but not aventurine feldspar |
| Tibetan sunstone, Tibetan andesine | May have been pale Mongolian andesine infused with copper (GIA) | 1.543 to 1.551 (IGS andesine) | 2.65 to 2.69 (IGS); 12.45 to 12.57 g | Treatment, per GIA’s account | Yes: andesine |
| Harts Range, Australia | Untwinned microcline microperthite with aventurine-type reflections (IGS) | α 1.520 to γ 1.527 (IGS) | 2.57; 12.22 g | Brownish-red hexagonal inclusions (IGS) | Yes |
| Moonstone, for contrast | Orthoclase with albite layers; adularescence, not aventurescence (GIA) | 1.518 to 1.526 (GIA) | 2.58; 12.25 g | None: layered light | Yes, but not sunstone |
| Aventurine glass, goldstone | Glittering glass (GIA 2025) | Not given | Not given | Not stated | No |
| Aventurine quartzite | Polycrystalline quartz with mica (GIA 2025) | Quartz: ω 1.544, ε 1.553 (sheet) | 2.65 (sheet); 12.45 g | Mica (GIA 2025) | No |
| Gold sheen sapphire | Corundum with aventurescence comparable to sunstone (GIA 2025) | Not given | Not given | Hematite, ilmenite and magnetite inclusions (GIA 2025) | No |
Is sunstone a feldspar? The definition in one sentence
Sunstone is feldspar showing aventurescence: a glitter from flat, reflective inclusions, in orthoclase, oligoclase or labradorite. GIA’s sunstone page says sunstone is a member of the feldspar group and that both the orthoclase and the plagioclase species boast a sunstone variety; its facts panel lists orthoclase, KAlSi3O8, and oligoclase and labradorite, a solid solution between NaAlSi3O8 and CaAl2Si2O8, with Mohs hardness 6.0 to 7.2. GIA’s description adds that the name sunstone refers to the gem’s appearance rather than to its chemical makeup, and that gemmologists call it aventurine feldspar when aventurescence is present.
Gemmology’s word, not mineralogy’s. GIA’s Gems and Gemology review of phenomenal gems (Summer 2025) says gem-quality aventurine feldspars are typically known as sunstones, after Andersen (1915). The September 2026 IMA-CNMNC Master List has rows for orthoclase, microcline, sanidine, albite and anorthite, and none for sunstone, oligoclase or labradorite; a whole-line scan finds 0 lines containing sunstone. A script over the 10 Handbook feldspar sheets cached here, from albite to anorthoclase, finds none that prints sunstone, aventur- or hematite. The species names for the plagioclase band are on oligoclase and labradorite.
So the answer is a qualified yes. Every stone the sources call sunstone is a feldspar; which feldspar is a separate question, and a stone sold as sunstone is only aventurine feldspar if it actually glitters. The two conditions are what the rest of this page tests.
Which feldspar is my sunstone? The three-band rule
The three-band rule: on GIA’s figures, a sunstone reading 1.518 to 1.526 is orthoclase, 1.537 to 1.547 oligoclase, and 1.559 to 1.568 labradorite. The bands are separated by 0.011 and 0.012, wide enough for a refractometer, and GIA gives birefringence of 0.005 to 0.008 for orthoclase and 0.007 to 0.010 for the two plagioclases. The International Gem Society adds that both the optic sign and the index vary between labradorite and oligoclase sunstone.
The scale agrees but by less. At GIA’s specific gravities, 2.58, 2.65 and 2.70, a 20.00 g piece reads 12.25, 12.45 and 12.59 g in water: steps of 0.20 g and 0.14 g, so a balance reading to 0.01 g separates the three bands only for clean, loose material. The method is on how to measure specific gravity at home.
The bands follow the hosts. On the Handbook sheets, orthoclase reads α 1.518 to γ 1.525, oligoclase α 1.533 to γ 1.552, and labradorite α 1.555 to γ 1.573; GIA’s oligoclase and labradorite bands sit inside those ranges, and its orthoclase band overruns the sheet by 0.001. The International Gem Society’s Oregon labradorite, Ab32An68 with α 1.559 to 1.563 and γ 1.569 to 1.573, starts inside the labradorite band and runs 0.005 above it. Why every plagioclase name is a composition band is on is labradorite a feldspar, and its An check is not repeated here.
What sunstone is not: goldstone, aventurine quartz, gold sheen sapphire
Aventurescence is an effect, not a mineral, and three non-feldspars show it. GIA’s 2025 review says the word aventurine comes from glittering glass, now called aventurine glass or goldstone, allegedly invented by accident in eighteenth-century Italy; that the name was first adopted in mineralogy for quartzite, a rock of polycrystalline quartz, containing glimmering mica; and that the best-known aventurescent mineral is aventurine feldspar. It defines aventurescence as specular reflection from isolated, visually discernible flat interfaces inside transparent minerals.
The three, separated. Goldstone is glass, not a mineral at all; see crystal vs mineral. Aventurine quartzite is quartz, with sheet indices ω 1.544 and ε 1.553: its ω falls inside the oligoclase band, so one reading does not separate them, and quartz’s uniaxial character does. The classification is on is aventurine a quartz. Gold sheen sapphire, GIA says, shows aventurescence comparable to that of sunstone, and it is corundum, hardness 9.
Moonstone is feldspar but not sunstone. GIA’s description says that although sunstone and moonstone are both feldspars, the resemblance stops there: moonstone’s phenomenon is adularescence, a soft glow, and sunstone’s aventurescence, a lively glitter. The moonstone pages are is moonstone a mineral and is labradorite a moonstone; their assets are not repeated here.
When the answer changes: Tvedestrand, Australia and Oregon
A locality name does not fix the feldspar. GIA’s review calls sodic sunstone mostly oligoclase, with the examples from Tvedestrand, Norway the most studied. The International Gem Society orthoclase article lists Tvedestrand for orthoclase sunstone, deep red-orange, in masses up to a few inches. Tvedestrand appears on the Handbook oligoclase sheet’s Distribution. Both sources call the material feldspar; they disagree on which.
Australia, documented the same way. GIA’s review names orthoclase sunstones from Australia and calls rainbow lattice sunstone from central Australia an orthoclase sunstone whose hematite films were originally magnetite. The International Gem Society sunstone article describes Harts Range, Northern Territory material as an untwinned microcline microperthite, α 1.520, γ 1.527, SG 2.57. This page does not say they are the same material. Either way it is a potassium feldspar, and the three-band rule puts both readings in the orthoclase band.
Oregon, and a label without glitter. GIA’s review says most Oregon sunstones are labradorites, and that all gem basaltic feldspars from Oregon are sold as Oregon sunstone even though not all show aventurescence. Such a stone is still feldspar, but not aventurine feldspar. GIA’s sunstone description also records the early-2000s controversy over Tibetan sunstone or Tibetan andesine, which laboratory findings indicated might have been pale andesine from Mongolia treated by infusion with copper.
Copper or hematite: what makes the glitter
Sunstone’s glitter comes from two kinds of reflector, metallic copper and iron oxides. GIA’s 2025 review says copper platelet inclusions in feldspar are rare and have been reported only in feldspar phenocrysts in certain basalts, as in Oregon sunstone, where they lie along the cleavage planes, mostly (010). Hematite sunstones, it says, are mostly found in granites or pegmatites and divide into orthoclase and sodic plagioclase, oligoclase or albite, distinguished by the shape and orientation of the hematite films. The International Gem Society’s sunstone article names hematite or goethite inclusions. Hematite and copper have species pages.
Size changes the look, not the answer. GIA’s description says small inclusions give a reddish or golden sheen over any bodycolour and larger ones glittery reflections, and that inclusions can be hematite, copper or some other mineral. This page gives no cause for sunstone bodycolours.
On this site, the classification questions are indexed at the collecting guides. This page gives no buying advice. Nothing on this site is offered for sale; the wanted list is the only commercial route.