Buergerite
Fluor-buergerite, NaFe3+3Al6(Si6O18)(BO3)3O3F
A rare iron-rich (ferric) species of the tourmaline group, dark brown to bronze-black, named after crystallographer Martin Buerger.
- Mohs hardness
- 7-7.5
- Color
- dark brown to bronze-black
- Type
- mineral
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Overview
Buergerite (more correctly fluor-buergerite) is a rare member of the tourmaline supergroup distinguished by ferric iron (Fe3+) in its structure, in contrast to the ferrous-iron schorl. It typically forms dark brown to bronze-black crystals.
It was named in honor of Martin J. Buerger, a noted American crystallographer. The species is uncommon and is primarily of interest to mineralogists and serious collectors rather than the gem trade.
Like other tourmalines it is a complex borosilicate, hard and durable, but its rarity and dark, opaque nature mean it is rarely cut as a gemstone.
Formation & geology
Buergerite forms in oxidized, boron-rich volcanic and metamorphic environments where ferric iron dominates over ferrous iron. Its type locality is Mexquitic in San Luis Potosi, Mexico, where it occurs in rhyolitic rocks.
The oxidizing conditions that stabilize Fe3+ over Fe2+ are key to producing buergerite rather than the more common schorl, and fluorine occupies a structural site giving the fluor-buergerite end-member.
The mineral remains rare, with few well-documented localities beyond the Mexican type locality.
How to identify it
Identify buergerite by its dark brown to bronze-black color, vitreous to submetallic luster, hardness of 7-7.5, and a pale brown to white streak. Crystals show the tourmaline group's striated prisms and rounded triangular cross sections.
A notable feature reported from type-locality material is bronzy iridescence on some surfaces.
Distinguishing buergerite from schorl and dravite by eye is difficult; positive identification generally requires chemical analysis to confirm the dominance of ferric iron and fluorine. Its volcanic rhyolite host and bronze sheen are helpful clues.
Uses & significance
Buergerite is essentially a collector's and research mineral, valued for completing tourmaline-group suites and for studying tourmaline crystal chemistry. It is rarely if ever used in jewelry because of its rarity and dark, opaque appearance.
Specimens from the Mexican type locality are sought by systematic mineral collectors.
It has no significant industrial or metaphysical market; its importance is scientific, illustrating the role of ferric iron in tourmaline-group chemistry.
Frequently asked questions
What is buergerite?
Buergerite (fluor-buergerite) is a rare ferric-iron member of the tourmaline supergroup, dark brown to bronze-black, named after crystallographer Martin Buerger.
How is buergerite different from schorl?
Schorl contains ferrous iron (Fe2+), while buergerite contains ferric iron (Fe3+) and fluorine, forming under more oxidizing conditions.
Where is buergerite found?
Its type locality is Mexquitic, San Luis Potosi, Mexico, where it occurs in rhyolitic volcanic rocks; it is rare elsewhere.
Is buergerite used as a gemstone?
No. It is too rare and dark for the gem trade and is valued mainly as a collector's and research mineral.
Buergerite guides
In-depth guides for identifying, valuing, and understanding Buergerite.
