Marcasite

This thumbnail specimen features a striking cluster of intergrown, euhedral marcasite crystals from the Dundas Limestone Quarry in southwestern Ontario. The crystals display a bright metallic golden sheen and sharp, well-developed crystal faces, giving the specimen an exceptional visual presence for its size. While this crystal has very minimal edge-wear and marcasite itself is not a rare mineral, specimens of this size and quality from this locality are decidedly uncommon, making this an especially aesthetic and desirable example.

The Dundas Quarry is a classic Ontario limestone locality, best known among collectors for producing a variety of well-crystallized sulfide minerals preserved within carbonate host rock. Marcasite occurs here as a secondary iron sulfide, often forming during low-temperature hydrothermal or diagenetic processes within the limestone. Although smaller or poorly formed marcasite is relatively common from the quarry, larger euhedral crystal groups with strong lustre and clean form, such as this specimen, are seldom encountered. The crisp crystal geometry, rich metallic colour, and overall balance of the intergrown crystals make it a standout thumbnail and an excellent representative of Ontario marcasite. It would make a strong addition to any collection focused on classic Canadian limestone localities, or sulfide minerals.