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Pyrite & Cookeite

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PDM571036

Pyrite & Cookeite

Description Tabs

Description
Locality: 
Ambas Aguas, Muro de Aguas, La Rioja, Spain
Class: 
Crystals on Matrix
Size Range: 
Small cabinet (7-10 cm)
Size: 
8.5 × 5.2 × 4.7 cm
Description

Well-formed shiny golden yellow pyrite crystals with the dominant cube {100}, modified by the pentagonododecaedron {210} that produce a nice striation in the cube faces. They are implanted on a marly matrix, and remarkably the crystals show asymmetric pressure-shadows that have been filled up by white cookeite.

On the contrary of what many collectors think, these pyrites are not sedimentary but have a metamorphic origin. Pressure-shadows are form when sediments are submitted to pressure. Because pyrite are not as easy to deform as the marly matrix, the sediment flows around the pyrite crystals creating openings around them. These openings were then filled up simultaneously by these white fibrous crystals of cookeite. A representative specimen for the locality and a not so easy to find example of asymmetric pressure-shadows. Nice!. It is from the collection of Manuel Urruchi, the Ambas Aguas mine owner. Collected in 2007-2008.

Mineral Data
What's on the rock

Pyrite

Formula: 
FeS2
Strunz: 
2.EB.05a
Crystal System: 
Isometric
Hardness: 
6.0 - 6.5

Cookeite

Formula: 
(Al2Li)Al2(AlSi3O10)(OH)8
Strunz: 
9.EC.55
Hardness: 
2.5 - 3.5
Streak: 
White
Type Locality: 
Mount Mica Quarry (Mount Mica Mine), Paris, Oxford Co., Maine, USA

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