Anhidrita
Anhidrita is a mineral with formula CaSO₄, in the Sulfatos group. This specimen comes from Naica, Naica, Saucillo, Chihuahua, México.
Description
Classic "Angel Wing" habit: sharply defined tabular and prismatic anhydrite crystals of sky-blue to pastel blue colour, with a very pearly lustre; a floater crystal, unabraded, with clean terminations. Well-formed anhydrite crystals are scarce worldwide; blue-coloured examples are a rarity.
History of this specimen
The piece comes from Sergio Petetrich, a novel-like figure of supposed blue blood who arrived from Italy on his yacht: he docked in Ferrolterra, fell in love with the place and stayed for good. On his death, his heirs disposed of the collection, selling it in bulk and in sealed boxes to the antique dealer Suso Vázquez. It was Suso who, the day we met, invited me to have the first look. That Sunday afternoon was like a lottery: I unwrapped hundreds of little packets. Everything suggested it was a secondary collection of duplicates and minor pieces, but I did find a small salvageable treasure. For example this anhydrite, also blue, like the supposed blood of its former owner.
About Anhidrita
Anhydrous calcium sulphate that crystallises in the orthorhombic system. It is "the stone that was thirsty" because it differs from gypsum by the absence of water in its structure and by its hardness and pearly lustre. Anhydrite is unstable in the presence of water; it absorbs moisture and converts to gypsum, increasing its volume by 60%. The best collector specimens come from hydrothermal deposits such as Naica, where they formed under high-temperature, low-humidity conditions.
About the locality
Famous for its giant gypsum crystals, Naica Mine was an anomaly. The workings lie well below the water table. To work there and extract lead and silver, the mining company (Peñoles) had to pump thousands of litres per minute of 58° water, 24 hours a day, every day of the year. In 2015 there was a partial flood. Metal prices fell at that time. With operations no longer profitable, the company switched off the pumps. Nature took over. The hot water (rich in sulphates and calcium) rose again and the Cave of the Crystals was submerged once more. No one can see the crystals now. At present, those 11-metre gypsum beams are in absolute darkness, continuously hydrated just as they were during the last 500,000 years before miners found them in 2000. Although it pains us not to visit them, the flood was the best thing that could have happened to them. The crystals were deteriorating. Their degradation has now stopped and, theoretically, they could grow again. And no, no more pieces from Naica will come out for a long time, perhaps never.
Technical data
- Catalogue No.
- 0265
- Composition
- CaSO₄
- Name
- Anhidrita
- Group
- Sulfatos
- Category
- Meritum Persé
- Mine
- Naica
- District / Municipality
- Naica
- Province
- Saucillo
- Region
- Chihuahua
- Country
- México
- Size (cm)
- 8 x 3 x 1.5
- Weight
- 36 g
- Ex-collection
- Sergio Petetrich
- Etymology
- From the Greek "anhydros", 'without water', referring to its difference from gypsum (CaSO₄·2H₂O).
- Quality
- Notable
- Value trend
- Al alza