Gem library
Jasper
Opaque chalcedony of a thousand landscapes
Jasper is chalcedony so loaded with impurities that it becomes fully opaque: up to 20 % iron oxides, clay or organic matter. It is less a mineral than a family of siliceous rocks, and the most varied in appearance in the whole mineral kingdom.
- Hardness (Mohs)
- 6.5 – 7
- Density
- 2.58 – 2.91
- Crystal system
- Trigonal
- Refractive index
- 1.530 – 1.540
- Cleavage
- None
Mineralogical identity
- Family
- Microcrystalline quartz — impure chalcedony
- Species
- Chalcedony
- Variety
- Jasper
- Chemical formula
- SiO₂ + oxides (up to 20 % impurities)
- Crystal system
- Trigonal (microcrystalline aggregate)
- Classification
- Semi-precious stone (rock)
- Rarity
- Very common
- Indicative price
- €0.10 – 3/ct
Etymology
From the Greek iaspis, itself from a Semitic root yashpeh, denoting a spotted stone.
Physical & optical properties
- Hardness (Mohs)
- 6.5 – 7
- Density
- 2.58 – 2.91
- Refractive index
- 1.530 – 1.540
- Cleavage
- None
- Fracture
- Splintery
- Lustre
- Waxy to dull
- Diaphaneity
- Opaque
- UV fluorescence
- None
- Pleochroism
- None
- Colours
- red, brown, yellow, green, multicoloured
Formation, geology & history
A rock rather than a mineral
Where agate stays translucent, jasper is charged with microscopic inclusions that block light: hematite for red, goethite for yellow and ochre, chlorite or actinolite for green, carbonaceous matter for black. Its density therefore varies more than other quartzes, up to 2.91 for very ferruginous varieties. Jaspers form by silicification of sediments or volcanic ash: the spectacular patterns of Oregon picture jasper trace ancient volcanic mud layers, and orbicular jaspers (Madagascar ocean jasper) reproduce crystallisation spherulites.
The main varieties
Trade vocabulary is abundant and often fanciful. The reliable names: red jasper (the classic, hematite), Australian mookaite (ochre, cream and plum), Madagascar ocean jasper (orbicular, multicoloured), picture jasper (brown bands evoking deserts), Dalmatian jasper (in fact an igneous rock, not a jasper), heliotrope or bloodstone (green flecked with red), kambaba jasper (fossiliferous, green-black). Beware of marketing names invented from nothing and applied to unremarkable rocks.
A millennia-old carving material
Its toughness — microcrystalline silica does not cleave and resists impact — makes it a material of choice for glyptics since prehistory. The Egyptians carved scarabs from it, the Romans intaglios, nineteenth-century Russian workshops monumental basins: the jasper basin in the Hermitage, cut from an Altai block, is more than five metres across. Today jasper is the stone of cabochons, pocket pebbles and tumbling, the barrel-polishing technique that produces the multicoloured pebbles of gift shops.
How to recognise it
- Complete opacityEven on a thin edge, jasper transmits no light. If a translucent rim appears, it is agate or chalcedony.
- Waxy, not vitreous, lustrePolished, jasper has a deep matt-waxy finish, less brilliant than agate. On fracture the look is dull and splintery.
- Scratches glassHardness 6.5-7 despite its earthy appearance. An opaque coloured rock scratched by a knife is more likely a mudstone, serpentine or calcite.
Imitations, treatments & confusions
- Dyed rocks sold under a jasper nameDyed howlite, marble or magnesite are frequently sold as exotic jaspers. Hardness test: these rocks scratch easily with a knife.
- Resin-reconstituted materialStone powder bound with resin and coloured. Light, warm, a plastic smell on the hot needle, and suspiciously repetitive patterns from bead to bead.
- Fanciful trade namesNot a material counterfeit but a descriptive deception: Dalmatian jasper (an igneous rock), kiwi jasper, zebra jasper… always ask for the actual mineral species.
Deposits & origins
Worldwide — India, Brazil, Madagascar, South Africa, United States (Oregon, Idaho: picture jaspers), Australia (mookaite), Russia (Ural jasper), France (Var and Provence jaspers)
Care & precautions
- Unaffected by water, salt and sun: wash in soapy water without worry.
- A dull polish is revived with fine paste; porous jaspers benefit from a light microcrystalline wax.
- Very tough, it withstands impact better than most stones — hence its use in sculpture.
- Ultrasonic-safe, except on reglued or resin-treated pieces.
Traditions & crystal healing
- Chakras
- Root (red jasper)
- Zodiac signs
- Aries · Virgo
- Element
- Earth
Tradition makes it the stone of the body and of endurance: red jasper is said to bring physical courage and grounding, green jasper regeneration, mookaite adaptability. It is credited with a «nurturing» role — the stone you keep in your pocket rather than display.
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
Jasper, agate or chalcedony: what is the difference?
One chemical family, three degrees of impurity. Chalcedony is translucent and plain, agate translucent and banded, jasper opaque and loaded with oxides.
Is Dalmatian jasper a jasper?
No. It is an igneous rock (a feldspar porphyry) speckled with black tourmaline. The name is purely commercial.
How do I spot dyed jasper?
Look for colour concentrated in cracks, an unreal saturation (turquoise, fuchsia) and a coloured deposit on damp cotton rubbed in a discreet spot.