Esfalerita
Esfalerita is a mineral with formula (Zn,Fe)S, in the Sulfuros group. This specimen comes from Mina Troya, Mutiloa, Gipuzkoa, Euskadi, España and joined the Terrium collection in 1980.
Description
Carpet of small, well-defined brown-amber sphalerite crystals, transparent and with adamantine lustre, covering most of the metallic matrix. At one end a colourless, transparent, doubly terminated quartz and a calcite crystal showing rhombohedral form stand out. The assemblage shows strong vitreous reflection and areas of high transparency under direct light.
History of this specimen
Its previous owner, Txomín, told me that in the late 1990s he had the good fortune to meet a miner who sold him about two hundred sphalerites from La Troya. Since then he insists this material must be handled with great care: clean them with alcohol and a brush, never with water, because being a sulphide its degradation can be reactivated. He even speaks of a bacterium involved in the process, and says that when the mineral begins to show a slight yellowish powder it is a sign it is already affected and there is no turning back in its degradation.
About Esfalerita
Sphalerite is the principal zinc ore mineral, often iron-rich, which imparts darker tones. In well-crystallised specimens it can reach gem quality and high lustre. It commonly associates with metallic sulphides in hydrothermal veins and is often found with quartz or dolomite, as in this case.
About the locality
Historic European reference locality. Worked by Exminesa between 1986 and 1993, when a collapse forced its closure. An underground lead-zinc working more than one kilometre long. Its large geodes—some several cubic metres—produced some of Spain's best sphalerites, much sought after for their transparency and honey-cognac colour. Closed and flooded since 2009; today only its tailings pond remains.
Technical data
- Catalogue No.
- 0199
- Composition
- (Zn,Fe)S
- Name
- Esfalerita
- Group
- Sulfuros
- Category
- Cupidium
- Matrix
- Matriz plúmbica
- Associations
- cuarzo calcita
- Mine
- Mina Troya
- District / Municipality
- Mutiloa
- Province
- Gipuzkoa
- Region
- Euskadi
- Country
- España
- Size (cm)
- 5.5 x 3.5 x 2.5
- Weight
- 70 g
- Acquired
- 1980
- Ex-collection
- Domingo Moreno (Txomín)
- Etymology
- From the German "Sphalerit", from Greek "sphaleros" ('deceptive'), for its resemblance to galena.
- Quality
- Muy buena
- Value trend
- Estable
Related specimens
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- Aerinita (fibrosa) — España
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