Gem library
Pietersite
Tiger's eye that went through a storm
Pietersite is tiger's eye and hawk's eye that were broken and then re-cemented by silica. The result no longer shows parallel fibres but whirls of blue and gold that seem to move beneath the surface, hence its nickname of tempest stone.
- Hardness (Mohs)
- 6.5 – 7
- Density
- 2.64 – 2.71
- Crystal system
- Trigonal
- Refractive index
- 1.534 – 1.540
- Cleavage
- None
Mineralogical identity
- Family
- Fibrous quartz
- Species
- Quartz
- Variety
- Silicified crocidolite breccia
- Chemical formula
- SiO₂
- Crystal system
- Trigonal (brecciated fibrous aggregate)
- Classification
- Semi-precious stone
- Rarity
- Rare
- Indicative price
- €2 – 50/ct
Etymology
Dedicated to Sid Pieters, the Namibian prospector who identified the deposit in 1962 and registered the material under that name.
Physical & optical properties
- Hardness (Mohs)
- 6.5 – 7
- Density
- 2.64 – 2.71
- Refractive index
- 1.534 – 1.540
- Birefringence
- up to 0.009
- Cleavage
- None
- Fracture
- Splintery
- Lustre
- Silky
- Diaphaneity
- Opaque
- UV fluorescence
- None
- Pleochroism
- None
- Colours
- blue, golden, red brown, steel grey
Formation, geology & history
A breccia, and what that means
To begin with, the same material as tiger's eye: fibrous crocidolite replaced by silica. But here a tectonic phase broke the rock into fragments, and each fragment ended up oriented differently from the others. Silica then re-cemented the whole. The geological term for a rock broken and then welded back together is a breccia, and that is exactly what pietersite is. Since the fibres are no longer parallel from one fragment to the next, chatoyancy no longer appears as a single band but in patches, in every direction: the stone looks full of contrary currents.
Two deposits, two eras
The original material comes from Namibia, identified in 1962 by Sid Pieters in an outcrop near Outjo. It is prized for its deep blues and vivid contrasts, and it is now practically exhausted: the Namibian pieces on the market come mainly from old stock, and their price follows. A second deposit was found in Henan province, China, in the early 1990s; it supplies most of today's pietersite, with redder and browner tones and less intense blues. Both are authentic pietersite, but they are neither the same origin nor the same price, and a serious dealer says which.
Cutting chaos
The lapidary cannot orient a pietersite as he would a tiger's eye, since there is no longer a single direction. He works by trial: he saws, looks at what the slice reveals, and chooses. One and the same rough stone can give a sumptuous cabochon and a dull one, depending on the plane of cut. The most sought-after pieces show several colours in a single cabochon, with patches lighting up in succession as it is tilted. Being quartz, the material is hard, tough and wears very well, which is rare for so spectacular a stone.
How to recognise it
- The whirlsChatoyant patches oriented every which way, separated by crisp boundaries. An ordinary tiger's eye has all its fibres parallel and a single band of light.
- The blue and gold contrastThe mixture of the two oxidation stages of iron, unoxidised blue and oxidised gold, in the same stone. A monochrome pietersite exists but is worth less.
- Quartz hardnessIt scratches glass without difficulty. A whirling stone that steel can scratch is glass or resin.
Imitations, treatments & confusions
- Tiger's eye dyed and artificially brecciatedCommon material treated to imitate the whirls. The boundaries between patches are too regular, and the dye concentrates in the fissures.
- Fibre glassA drawn multicoloured glass. Too bright, warm to the touch, and the patterns repeat from one bead to the next.
- Chinese sold as NamibianBoth are authentic. The Namibian, deep blue, is worth several times the Chinese, which is redder. Origin is worth asking about.
Deposits & origins
Namibia (Kuruman and Outjo: the original deposit, now almost exhausted), China (Henan, the material in the trade today)
Care & precautions
- Warm soapy water and a soft cloth, a brief rinse and immediate drying.
- Avoid ultrasonics: the stone is a breccia, hence crossed by natural planes of re-cementing.
- Fears neither light nor ordinary heat, unless it has been dyed.
- Store separately, the silky polish scratches and the reflections go out on a matt surface.
Traditions & crystal healing
- Chakras
- Third eye · solar plexus
- Zodiac signs
- Leo · Scorpio
- Element
- Fire
Nicknamed tempest stone, it is associated with courage in change and with getting through turbulent periods, by direct analogy with its appearance. 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
Pietersite or tiger's eye?
The same starting material, but pietersite was broken and then re-cemented: its reflections run in every direction, whereas tiger's eye has a single band of light.
Why do prices vary so much?
Two deposits. The Namibian, deep blue, is almost exhausted and dearly paid for; the Chinese, redder, is common and affordable. Ask about the origin.
Can it be worn every day?
Yes. It is quartz, hardness 7 and no cleavage. It is one of the few very spectacular stones that stand daily wear.
Tools for this stone
Pietersite: only the tools this stone actually concerns, each carrying the value read on this page.