Octahedral sylvite crystals in a Colombian emerald

Interesting micrograph in a Colombian emerald. This natural cavity, filled with a salted solution (brine), hosts two large crystals that are most likely sylvite. Sylvite is a potassium chloride (KCI), while halite is a sodium chloride (NaCl). Sylvite can be recognised owing to the truncations at the corners of the cube, which favour an octahedral habit, with Miller indices for the faces of the octahedron {111}. Halite does not have these truncations, either as a result of its growth or by cleavage, as its cleavage is perfect according to the faces of the cube, with Miller indices of {100}.⁠

• Micrograph: Guillaume Zuber (2025), GGTL Laboratories Switzerland ⁠

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