Esfalerita Marmatita
Esfalerita is a mineral with formula (Zn,Fe)S + FeS₂, in the Sulfuros group. This specimen comes from Stan Terg Mine (Stari Trg), Trepča Complex, Mitrovica, Mitrovica District, Kosovo and joined the Terrium collection in 2025.
Description
The Oxidised Sister. Dominated by three large black sphalerite (var. Marmatite) crystals of tetrahedral habit and adamantine lustre. They sit on a stepped, golden pyrite matrix (pseudomorph after pyrrhotite) that preserves the original hexagonal geometry. Small scattered white quartz needles contrast with the dark sulphides.
History of this specimen
These pieces with large, well-formed sphalerite crystals, with pyrite and quartz, are sought after and scarce in this size and quality. Specimens like this, where the replacement preserves the original massive texture of pyrrhotite, are uncommon even in the best historical lots. In June 2025 I washed the piece with water to remove dust and, unknowingly, triggered oxidation of the matrix. Within a few weeks it lost lustre and greyish areas appeared. I tried to halt it by immersing it in alcohol, though I later learnt that was not suitable either. Supposedly I must from now on keep it in an airtight box with silica gel to keep it dry and stabilise it. For the moment, o have managed it and it has regained the brightness and lustre it had. I probably overreacted.
About Esfalerita
Pyrrhotite is the magnetic 'pyrite' that lacks part of the iron needed to be pyrite; it starts as a defective pyrite and, instead of forming cubes, tends to form hexagonal crystals or granular masses. Bronze to brown in colour, darker than pyrite. It tarnishes (oxidises) much faster. As for the other two minerals: pyrite is iron sulphide, the principal ore of iron. Sphalerite is zinc sulphide, the primary ore of zinc. The marmatite variety of sphalerite is iron-rich, which gives it an opaque black colour.
About the locality
The Stari Trg Mine in the Trepča Complex is a world-class classic locality for sulphides; Trepča, worked since Roman times and affected by recent conflicts, yields few pieces with large, well-formed sphalerite crystals, much sought after for their aesthetics.
Technical data
- Catalogue No.
- 0129
- Composition
- (Zn,Fe)S + FeS₂
- Name
- Esfalerita
- Variety
- Marmatita
- Group
- Sulfuros
- Category
- Cresta Montis
- Matrix
- Pirita pseudomorfa tras Pirrotita
- Associations
- cuarzo
- Mine
- Stan Terg Mine (Stari Trg)
- District / Municipality
- Trepča Complex
- Province
- Mitrovica
- Region
- Mitrovica District
- Country
- Kosovo
- Size (cm)
- 10.8 x 7.3
- Weight
- 733 g
- Acquired
- 2025
- Etymology
- The name of this mineral is a fossilised miners' insult. Early German miners called it "Blende" (from the verb blenden, 'to deceive') because its lustre promised good metals (lead or silver), but when smelted for value... nothing good came out. Official science kept the slight: in 1847 it was named sphalerite, from the Greek 'sphaleros', literally 'treacherous'. It is the spiritual sister of pitchblende; another slighted name, and two 'lying' minerals that frustrated generations of miners. The variety marmatite is named after Marmato (Colombia).
- Quality
- Notable
- Value trend
- Estable
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- Esfalerita (Cleiofana o Blenda acaramelada) — España
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