• An aragonite and calcite specimen in indirect sunlight. It is a chunky triangular-shaped piece with the front covered with opaque matte rough-textured points, in a light tan color that darkens to a light brown at the base.
  • Closer view of the points on the piece, shaped like typical calcite points but with a textured layered mineral overgrowth layer.
  • A side-view of the piece, showing the points are on a crust-like layer on top of the matrix, with hollow growth underneath.
  • Detail of the points, with the crust appearing composed of flat platelets of growth. A broken crystal at the corner shows a triangular crystal inside a ring of brown and then light crust.
  • The back of the piece, shaped like a large slice of pie with a textured flat surface and botryoidal growth along the rim.
  • A side of the piece that is textured and mostly flat, and half-covered with an unattractive white overgrowth layer.
  • Detail of the botryoidal growth on the back, with a rim of botryoidal growth raised away from the surface. On the left edge, the spheres form a zig-zag edge.
  • Detail of the botryoidal growth, the spheres of which appears composed of small blades oriented in different directions.
  • Detail of a cluster of crystals inside a hollow of the crust on the specimen.
  • Scale image of the piece on a measuring mat, measuring about two and a quarter inches long and two inches wide.
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Aragonite and calcite with botryoidal side

Aragonite and calcite with botryoidal side

$18.00 USD
$18.00 USD
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Locale: Sidi Ayed, Fès-Meknès Region, Morocco

Approx dimensions: 2.25 x 2 x 1.5"

Approx size: 185g

 

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. It appears aragonite formed over calcite points which then partially dissipated, leaving some hollow between layers. There is an odd crystal formation inside this hollow. On the other side, the aragonite has formed more botryoidal growth composed of a blade-like structure.

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