Carrollite - Lustrous Cuboctahedral Crystal on Dolomitic Matrix, DR Congo

Carrollite from the Kamoya South II Mine in the Kambove district of Haut-Katanga is the standard by which the species is judged worldwide. Nothing else on earth produces this thiospinel in sharp, mirror-bright, free-standing crystals of collector size, and this piece shows precisely why the locality earned that reputation: a single robust individual measuring 3.1 by 2.8 centimetres, perched upright and fully exposed on a pale carbonate matrix that could hardly provide a better foil for its metal. The habit is cuboctahedral, with the octahedral faces dominant and the cube faces reduced to clean, finely bevelled truncations along the edges. Seen from the front the crystal presents as a broad, almost shield-like polygon, the geometry crisp and unambiguous, each facet meeting its neighbour along a straight edge. It stands proud of the matrix rather than being half-buried, so the eye reads the full three-dimensional form, and the small accessory crystal nested at its base reinforces the sense of a natural, unforced composition. Colour in Carrollite is a matter of the surface alone: a pale steel-grey with a faint warm, creamy cast, the tone of polished pewter rather than the bluish tin of Galena. Here the larger faces carry a light frosting of growth texture and very subtle striations, while the narrow bevels along the edges read noticeably darker and sharper, giving the crystal internal contrast as it is turned. The lustre is frankly metallic and strongly reflective, and under directional light the broad octahedral face behaves almost as a mirror, flaring bright and then dropping to gunmetal as the angle shifts. The matrix is a pale, buff-to-pinkish carbonate rock flecked with darker sulphide grains and a small olive-gold patch toward the right side, with coarse white carbonate crystals along the upper margin. It is rough, dusty and unpretentious, exactly the kind of backdrop against which a bright metallic crystal reads most strongly; there is no competition for attention. Condition is reported as overall good, with the Carrollite stabilised on the matrix and light chatter on a couple of crystal edges. That is worth stating plainly, because in this species the edges and face junctions are the whole game: Carrollite is brittle, the bevels are thin, and any bruise registers as a bright white scar against the grey. The principal display faces here are intact and the damage is confined to edge contacts. At 7.3 by 6.6 by 5.3 centimetres this is a small cabinet specimen, and it carries the presence of a larger piece because the crystal sits at the visual centre with nothing crowding it. Provenance from the John Warn collection adds a further layer of interest. Under a single raking light the Carrollite ignites against the pale rock, and the composition resolves instantly.