Gem library
Sunstone
The feldspar that throws copper sparks
Sunstone takes its name from the orange flash that runs beneath the surface as you turn it. That flash is not a colour but a reflection: thousands of microscopic platelets, aligned inside the crystal, catch the light all at once.
- Hardness (Mohs)
- 6 – 6.5
- Density
- 2.62 – 2.67
- Crystal system
- Triclinic
- Refractive index
- 1.537 – 1.547
- Cleavage
- Perfect on {001}
Mineralogical identity
- Family
- Plagioclase feldspars
- Species
- Oligoclase (sometimes labradorite)
- Variety
- Heliolite, aventurescence
- Chemical formula
- (Na,Ca)AlSi₃O₈
- Crystal system
- Triclinic
- Classification
- Semi-precious stone
- Rarity
- Common
- Indicative price
- €1 – 60/ct (faceted Oregon: far beyond)
Etymology
Heliolite, from the Greek helios, «sun», and lithos, «stone», by symmetry with moonstone, its exact counterpart in the same feldspar family.
Physical & optical properties
- Hardness (Mohs)
- 6 – 6.5
- Density
- 2.62 – 2.67
- Refractive index
- 1.537 – 1.547
- Birefringence
- 0.007 – 0.010
- Cleavage
- Perfect on {001}, distinct on {010}
- Fracture
- Uneven
- Lustre
- Vitreous
- Diaphaneity
- Transparent to translucent
- UV fluorescence
- None
- Pleochroism
- Weak
- Colours
- orange, red, copper, honey yellow, green
Formation, geology & history
Aventurescence, and where it comes from
The effect has a name, aventurescence, by analogy with aventurine. It arises from flat, oriented inclusions that reflect light in concert. In Norwegian and Indian sunstone those inclusions are platelets of hematite or goethite, red to brown. In Oregon material they are flakes of native copper, a case unique in the world: the copper exsolved from the feldspar as a lava flow cooled slowly. It is that copper which gives the best Oregon stones a frank red or green colour, and which makes them worth faceting rather than cutting as cabochons.
Formation and geology
Plagioclase feldspars crystallise in igneous rocks, so sunstone turns up in basalts, syenites and certain pegmatites. The Ponderosa deposit in Oregon works basalt flows in which the crystals, torn from depth and carried up by magma, are freed by weathering: they are picked out of the decomposition clay. In Norway, at Tvedestrand, the stone comes from pegmatites, and that is the material nineteenth-century mineralogists described. India supplies most of the ordinary trade cabochons, with red-brown goethite inclusions.
One family, two stones
Sunstone and moonstone are both feldspars, and the kinship is more than a commercial pun. Moonstone is an orthoclase with albite exsolution, whose lamellae scatter light into a bluish sheen: that is adularescence. Sunstone is a plagioclase with metallic inclusions whose platelets reflect it: that is aventurescence. A diffuse veil on one side, a pinpoint sparkle on the other. The two effects can coexist in a single crystal, and some Indian stones show both.
How to recognise it
- The sparkle movesTilt the stone under a lamp: the flash should slide and light up in patches. A uniform orange that does not move is not aventurescence.
- Platelets under a loupeAt 10× you can make out individual flakes with sharp outlines, all lying in one plane. In a glass imitation the flakes are scattered at random and face every direction.
- Feldspar cleavageOn a rough edge, two cleavage planes meet at very nearly a right angle, with a pearly sheen. That is the family's signature.
Imitations, treatments & confusions
- Aventurine glass (goldstone)The reigning imitation, invented in Murano: a glass loaded with copper flakes. It is too regular, too bright, the flakes are identical and point every which way, and a bubble usually lurks somewhere in the mass.
- Dyed feldsparWashed-out cabochons dyed orange. The dye lodges in the cleavages, visible under a loupe as darker lines.
- Oregon claimed wronglyOregon provenance multiplies the price. A faceted red or green stone sold as «Oregon» without paperwork deserves a question: copper inclusions are visible under a loupe, hematite ones are not.
Deposits & origins
United States (Oregon, the only source of facetable stone with native copper inclusions), India, Norway (Tvedestrand, the historic deposit), Canada, Russia, Tanzania, Madagascar
Care & precautions
- Warm soapy water and a soft brush, rinsed briefly. Dry at once.
- No ultrasonics: the double cleavage copes badly with them, especially on an included stone.
- Takes daylight without fading, unlike many orange stones.
- Store separately: at hardness 6 it is scratched by quartz and anything harder.
Traditions & crystal healing
- Chakras
- Solar plexus · sacral
- Zodiac signs
- Leo · Aries
- Element
- Fire
Associated with drive, warmth and the return of energy after a low period, it is paired with moonstone in most handbooks, one for the day and one for the night. The Vikings are said to have used it, but the famous «sunstone» of the sagas is more probably Iceland spar, a calcite. Cultural heritage, never medicine.
The virtues described here belong to tradition and cultural heritage. They are in no way medical advice and never replace a consultation.
Frequently asked questions
Sunstone and aventurine, what is the difference?
Aventurine is a quartz with fuchsite flakes, usually green. Sunstone is a feldspar with metallic flakes, usually orange. The optical effect shares a name, the minerals have nothing in common.
Why do some cost a hundred times more?
Faceted Oregon stones, transparent, red or green, with visible copper, are rare and sought after. An opaque Indian cabochon belongs to another market.
Does it fear sunlight?
No. It is one of the few coloured stones that does not fade, its colour coming from inclusions rather than a fragile colour centre.
Tools for this stone
Sunstone: only the tools this stone actually concerns, each carrying the value read on this page.