• An aragonite and calcite specimen in indirect sunlight. it is a rectangular wedge-shaped piece with the front covered with matte opaque rough-textured points, in a light tan color that darkens to light brown at the base of the specimen.
  • A side-vide of the piece, with matrix visible on the side and a gap between it and the crust-like layer of points on the top.
  • Closer view of the points on the piece, shaped like typical calcite points but with a textured layered mineral overgrowth layer.
  • Side-view of the piece, showing the hollow under the crust on top.
  • The backside of the piece, with a botryoidal pattern of spherical growth along the top edge with less definition toward the center of the piece.
  • Detail of the botryoidal growth on the back, with a rim of botryoidal growth raised away from the surface. The spheres appear composed of small blades oriented in different directions.
  • Looking down the edge of the piece, with the botryoidal edge in the foreground and the pointed side on the top.
  • The sides of the piece, a rough pale matrix without crystal development.
  • Scale image of the piece on a measuring mat, measuring almost three inches long and two inches wide.
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Aragonite and calcite with botryoidal side

Aragonite and calcite with botryoidal side

$24.00 USD
$24.00 USD
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Locale: Sidi Ayed, Fès-Meknès Region, Morocco

Approx dimensions: 3 x 2.75 x 2"

Approx size: 480g (1 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 some hodgepodge of the above.

Which is all to say, this specimen falls somewhere in that ‘hodgepodge’ category. It appears aragonite formed over calcite points which then partially dissipated, leaving some hollow between layers. On the other side, the aragonite has formed more botryoidal growth composed of blade-like growth. There are dark greenish spots of another mineral embedded in the matrix.

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