• An irregularly-shaped mineral specimen composed of several minerals. At the top is a sheet of parallel thin flat selenite crystals. A crust of golden siderite grows on and between the selenite.
  • Detail of colorless selenite, parallel crystals with slanted ends like blinds.
  • The piece held in indirect sunlight, in a hand to show hand-sized scale.
  • The back side of the piece held in indirect sunlight, the colorless selenite appearing almost white against golden siderite and shiny pyrite.
  • A side of a mineral specimen covered with selenite crystals angled in different directions. Near the center of the image several curved selenite crystals are visible.
  • Side-view of the dozens of small selenite crystals, icy colorless with high luster. The siderite is lumpy and opaque
  • Detail of selenite crystals pointed in all directions. On the left edge is a small cube formation covered with light mineral.
  • A view of the sheet of parallel selenite crystals, with translucency showing the rough surface of the siderite below.
  • The sheet of selenite crystals at an angle reflecting light, showing the parallel growth lines and angled ends
  • Detail of fine parallel selenite crystals reflecting light, with one split and splayed on the end
  • The underside of the specimen, a conglomerate of different minerals including a dull dark gray galena and a shiny gold pyrite, with golden siderite sprinkled across the surfaces.
  • Detail of a large hexagonal barrel shaped mineral covered with other minerals, including small dots of yellow mineral along planes on the surface.
  • Detail of the large hexagonal barrel crystal, showing unusual clusters of shiny pyrite on the end and side.
  • Scale image of the piece on a measuring mat, measuring a bit over four inches long by three inches wide.
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Selenite crystals and siderite with pyrite pseudomorph base

Selenite crystals and siderite with pyrite pseudomorph base

$50.00 USD
$50.00 USD
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Locale: Potosí Mine, Santa Eulalia, Chihuahua, Mexico

Approx dimensions: 4 x 3 x 2.5"

Approx weight: 490g (1 lb)

 

This specimen is a sampler mix of minerals from the Potosí Mine, with selenite and light-to-orange-yellow siderite on a heavy base composed of several minerals. Selenite is the crystal-clear form of gypsum, though the two terms are often used interchangeably. Selenite is one of the more common minerals to come from Mexico, which is known for the nearby Naica locale. This selenite shows typical twinned and fishtail growth habits.

The heavy base is pyrite, pyrrhotite, and galena. The large hexagonal formation is characteristic of pyrrhotite, a mineral that looks quite similar to pyrite. Pyrite from the Potosí Mine is known to pseudomorph after pyrrhotite in this hexagonal formation, which appears to have occurred with this specimen. Pyrrhotite is supposed to have some slight magnetism, and this piece—like pyrite—does not seem too. Shining masses of pyrite grow on its surface and have rosette-like growth.

Near the 'top' back there is a chunk of dark gray mineral with cubic surface patterning I suspect to be galena because it commonly accompanies pyrite, pyrrhotite, and siderite from this locale. The galena has formed a small flat square tabular crystal coated in overgrowth, visible on the front of the specimen.

UV reactivity Under 365nm UV light, the selenite fluoresces an icy blue color in patchy areas of the back.

** Brittle warning: Selenite is soft and can easily break, flake, or bend. There are several crystals with curvature which I believe is damage that occurred to the specimen, not natural bending. Handle this specimen by the heavy base to avoid damage.

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