• An aragonite and calcite specimen in indirect sunlight. it is an irregular-shaped piece with the front covered with matte opaque rough-textured points, in a light tan color that darkens to light brown at the edges of the specimen
  • Closer view of the points on the piece, shaped like typical calcite points but with a textured layered mineral overgrowth layer. The tip of one large point is open, showing it is hollow inside.
  • A side-view of the specimen, showing the layer of points has a crust-like edge with hollow and irregular honeycomb-like growth underneath
  • Angled view of the back and bottom of the specimen, both a rough crusty surface. There is a pocket on the junction between faces, with small crystals visible inside.
  • The back of the piece, covered with crusty white mineral growth over a light yellow mineral. The pocket on the corner appears as a cut-out on the bottom right.
  • Detail of the bottom of the piece with a white semi-opaque crust with geometric edges and rhombohedral shapes in the pockets in the center of it.
  • Detail of the crusty structure of the back, with pockets of glossy crystal in honeycomb growth. At the top, the points are visible and there is hollow under the edges of the crust where the points begin.
  • Detail of the pockets of glossy crystal in the white crust on the bottom of the piece, with a light yellow color and good translucency.
  • Detail of the crystal pocket on the back of the specimen, with small white rhombs scattered among irregular glassy crystal growth.
  • Close detail of the pocket on the back, howing the rhombohedral shape of the small white calcite crystals.
  • The specimen illuminated in UV light, with patchy peach-red glow. The pocket fluoresces well.
  • Scale image of the piece on a measuring mat, measuring about three and a half inches long and a bit over two inches wide.
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Aragonite and calcite with pocket of calcite rhombs

Aragonite and calcite with pocket of calcite rhombs

$26.00 USD
$26.00 USD
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Locale: Sidi Ayed, Fès-Meknès Region, Morocco

Approx dimensions: 3.5 x 2 x 2"

Approx size: 425g (0.9 lb)

 

Calcite and aragonite are polymorphs of one another, meaning that the same chemical composition (calcium carbonate) has crystallized into different crystal structures (trigonal and orthorhombic, respectively). Calcite and aragonite often grow together, and the two minerals are also frequent paramorphs of one another—a pseudomorph of the same chemical composition and retaining the original crystal shape but with different crystal structure, created through a change of conditions such as heat or pressure. There is understandably some confusion distinguishing what is calcite, versus aragonite, or a paramorph, or some hodgepodge of all of the above.

Which is all to say, this specimen falls somewhere in that ‘hodgepodge’ category. The matrix is partially calcite, and rhombohedral patterns can be seen in places. It appears aragonite formed over calcite points on the top which then partially or wholly dissipated, leaving some of the aragonite points hollow. There is a small pocket on the back of the piece filled with small white calcite rhombs.

UV reactivity The aragonite will give a moderate reaction under 365 nm UV light, fluorescing a light taupe color. The calcite will stand out in comparison, fluorescing a strong peachy-red color.

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