Gem library
Bronzite
The pyroxene with a hot-metal sheen
Bronzite owes its name to the warm metallic sheen that runs along its cleavage planes. It is not a colour but a reflection: microscopic lamellae of iron oxide, trapped during cooling, return light like a satin mirror.
- Hardness (Mohs)
- 5 – 6
- Density
- 3.20 – 3.40
- Crystal system
- Orthorhombic
- Refractive index
- 1.665 – 1.703
- Cleavage
- Distinct on {110}
Mineralogical identity
- Family
- Silicates, inosilicates, pyroxene group
- Species
- Enstatite
- Variety
- Ferroan enstatite with schiller
- Chemical formula
- (Mg,Fe)₂Si₂O₆
- Crystal system
- Orthorhombic
- Classification
- Semi-precious stone
- Rarity
- Common
- Indicative price
- €0.20 – 4/ct
Etymology
From the bronzy sheen of its cleavage surfaces, described as early as the eighteenth century. It is not a species name: bronzite is a ferroan enstatite.
Physical & optical properties
- Hardness (Mohs)
- 5 – 6
- Density
- 3.20 – 3.40
- Refractive index
- 1.665 – 1.703
- Birefringence
- 0.010
- Cleavage
- Distinct on {110}, two directions at 88°
- Fracture
- Uneven
- Lustre
- Submetallic, bronzy
- Diaphaneity
- Opaque
- UV fluorescence
- None
- Pleochroism
- Weak
- Colours
- brown, bronze, golden brown, green brown
Formation, geology & history
A pyroxene from the mantle
Enstatite is a magnesian pyroxene, one of the most abundant minerals in the Earth's mantle and a common constituent of stony meteorites. Bronzite is its intermediate variety, in which about a fifth of the magnesium is replaced by iron. It is found in basic and ultrabasic igneous rocks, gabbros, norites and peridotites, and in certain metamorphic schists. The Styrian deposits in Austria are the ones that gave the name, but most ornamental material now comes from South Africa and Brazil, where large compact masses are worked.
Schiller, and where it comes from
The bronzy sheen carries a German name that passed into mineralogical vocabulary: schiller. It arises from lamellar inclusions of ilmenite, magnetite or hematite, exsolved during the slow cooling of the rock and oriented parallel to the pyroxene's cleavage planes. Light striking those planes is reflected from thousands of lamellae at once, which gives a continuous satin sheen rather than a pinpoint glitter. The phenomenon is of the same family as sunstone's, but here the orientation is imposed by the cleavage, not by free growth.
Working and uses
Bronzite is cut into cabochons, spheres and beads, and its polish is warm, deep, pleasant in the hand. It is often displayed alongside seraphinite, astrophyllite and sunstone, for the kinship of their sheens. Its moderate hardness, 5 to 6, and its double cleavage make it a pendant stone rather than a ring stone. It is regularly confused with hypersthene, a neighbouring pyroxene richer in iron and darker, whose exact distinction requires analysis: the two are sold interchangeably, and that matters little as long as nobody claims otherwise.
How to recognise it
- The continuous sheenSchiller is a sheet of light sweeping the surface, not a scatter of points. Aventurine and aventurine glass glitter in separate flakes.
- Cleavages at 88 degreesOn a fracture, two families of bright planes meet at very nearly a right angle. That is the pyroxene signature, and it distinguishes bronzite from the amphiboles, whose cleavages meet at 120 degrees.
- Density3.3: distinctly heavier than a brown quartz or a jasper of the same size. The difference is felt in the hand.
Imitations, treatments & confusions
- Brown aventurine glassBrown goldstone. Regular flakes oriented every which way, bubbles, and a density of 2.5 instead of 3.3.
- Hypersthene sold as bronziteA neighbouring pyroxene, darker. A good-faith confusion in almost the whole trade, with no consequence for the price.
- Dyed brown jasperNo schiller, no cleavage, hardness 7. The sheen is the test.
Deposits & origins
Austria (Styria, the classic deposit), South Africa, Brazil, United States, Greenland, India
Care & precautions
- Warm soapy water and a soft cloth, a brief rinse and drying.
- No ultrasonics: the double cleavage and the inclusion lamellae make it a stone sensitive to vibration.
- Fears neither light nor ordinary heat.
- Store separately, the polish scratches and the schiller loses its lustre on a dulled surface.
Traditions & crystal healing
- Chakras
- Root · solar plexus
- Zodiac signs
- Taurus · Leo
- Element
- Earth
A stone of grounding and recentring, often recommended to accompany «higher» stones such as amethyst, in the idea of balancing. Its reputation is recent and owes much to its colour. 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
Bronzite or hypersthene?
Bronzite is more magnesian and lighter, hypersthene more ferroan and darker. The boundary is conventional, and the trade mixes them. No practical importance.
Can the sheen disappear?
Only if the polish degrades. Schiller is an internal property, it does not fade, but it shows only on a clean surface.
Can it be worn as a ring?
Better avoided. Hardness 5 to 6 with two cleavages: the edges blunt and the polish dulls quickly on a hand.
Tools for this stone
Bronzite: only the tools this stone actually concerns, each carrying the value read on this page.