Esfalerita
Esfalerita is a mineral with formula ZnS, in the Sulfuros group. This specimen comes from Mina Troya, Mutiloa, Gipuzkoa, Euskadi, España and joined the Terrium collection in 2000.
Description
Floater aggregate of sphalerite with wide colour variation and readable growth stages. It includes black marmatite of larger size, followed by later generations in honey, cognac and green tones, with olive highlights, and a final sprinkling of very vivid small yellows. Beside two dolomite rhombohedra growing on marmatite, one of those yellows shows a perfect tetrahedral habit and is completely gemmy. Excellent under a loupe. Faces mostly curved and without breaks.
History of this specimen
Txomín told me he obtained this piece in the late 1990s, when he happened to meet a miner who sold him a large lot—about two hundred sphalerites—from the Troya Mine. He always insisted these pieces should not be washed with water but with alcohol, reminding me that, after all, they are sulphides.
About Esfalerita
Sphalerite is the principal zinc mineral, often iron-rich, which gives it darker tones. In well-crystallised specimens it can reach gem quality and high lustre. It typically associates with metallic sulphides in hydrothermal veins and is commonly found with quartz or dolomite, as in this case.
About the locality
A historic European reference. The last significant deposit discovered in the Basque Country, in 1972. Worked by Exminesa between 1986 and 1993, when a collapse forced its closure. An underground lead–zinc gallery more than one kilometre long. Its large geodes (even several cubic metres) produced some of the best sphalerites in Spain, prized for their transparency and honey–cognac colour. Closed and flooded since 2009, its settling pond (sludge) has recovered fully and today is an important ornithological site.
Technical data
- Catalogue No.
- 0326
- Composition
- ZnS
- Name
- Esfalerita
- Group
- Sulfuros
- Category
- Cupidium
- Associations
- dolomita
- Mine
- Mina Troya
- District / Municipality
- Mutiloa
- Province
- Gipuzkoa
- Region
- Euskadi
- Country
- España
- Size (cm)
- 7 x 4 x 3
- Weight
- 84.4 g
- Acquired
- 2000
- Ex-collection
- Domingo Moreno (Txomín)
- 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 affront: in 1847 it was named Sphalerite, from the Greek "sphaleros", literally 'treacherous'.
- Quality
- Muy buena
- Value trend
- Al alza
Related specimens
- Abellaíta — España
- Abernathyita — España
- Abernathyita — España
- Abernathyita — España
- Acantita (Paramórfica tras Argentita) — Marruecos
- Aerenita — España
- Aerinita (fibrosa) — España
- Analcima — España