Nb₁₂S₁₆Sr

Architectural potential

A niobium-rich strontium polysulfide cast at 130 °C, this pushes the zero-kiln compression argument up to 150 MPa — three times the iron-sulfide sibling — bringing it into the range where non-reinforced pavement blocks, cast cladding panels for gallery interiors, and stair-tread inlays become structurally reasonable. Like its family, the body forms through chemistry rather than firing, so the eighty-nine-per-cent cut in embodied CO₂ against Portland cement is the lead argument. Natural placements are signature cast slabs in zero-kiln workshops, heavy gallery thresholds where weight-in-the-hand is part of the curatorial register, and cast sills or plinths in retrofit interventions where a kiln cannot be lit but a geological presence is wanted. Two kilograms of workshop ceiling constrains it to detail and insert scale rather than whole-wall work. The real caveat is cost: at €94.40 for a 500 g batch, niobium drives the price roughly twenty times higher than the iron-sulfide sibling, and the supply-chain score sits at 0.29 because niobium comes from a small number of producing regions. Specification belongs in the signature-element register — a single threshold, a named bench, a plinth with a story — rather than repeated bulk tiling.

Material character

The 70×70×40 mm slab reads a deeper yellow-orange than the iron-sulfide siblings — the niobium pulls the matrix toward a mustard-amber with subtle olive shadows at the edge. Surface mold-matte with a finer meniscus than the coarser iron polysulfides; the denser niobium-strontium matrix casts a tighter, more even skin. Edges come as-cast, with a small bead where the mold parting left a seam. At 5.16 g/cm³ the slab resists a single-handed lift and sits firmly on the bench — noticeably heavier for its size than the 4.0 g/cm³ iron sibling, and the density difference is legible in the hand rather than only on paper.