Garnet (Andradite-Grossular series) (Specimen #100288)

Mineral(s):     Garnet (Andradite-Grossular), Epidote, Quartz, Magnetite)

Location:  Marmoraton Iron Mine, Marmora Township, Hastings County, Ontario

Size:    9.5 x 6.0 x 2.2 cm

Provenance: Reiner Mielke, Jeffrey Shallit

Description: This superb specimen features numerous andradite-grossular garnets with bright luster in association with rosettes of epidote on quartz and bladed magnetite. The garnet crystals are primarily dark red brown trapezohedron-dodecahedron form with several trapezohedron crystals. The crystals are very well-formed and deep in colour. The red garnets, green epidote and black magnetite create an attractive colour palette. There are a couple of ‘contact’ marks on the specimen, otherwise the condition is excellent.

The Marmoraton Iron Mine, located near Marmora in Hastings County, Ontario, was a significant open-pit operation active from 1955 to 1978. It was developed by the Marmoraton Mining Company, a subsidiary of Bethlehem Steel, to extract high-grade magnetic iron ore from Precambrian meta-sedimentary rocks beneath a thick limestone cap. The geology of the area is rich and complex, featuring metabasalt, felsic rocks, and marble, alongside metallic deposits of iron, copper, nickel, silver, and gold. Mineral collectors are drawn to the site for its diverse specimens, which include magnetite, hematite, pyrite, actinolite, epidote, and its striking garnet specimens. Almandine garnets from this site typically exhibit deep reddish hues and form within the metamorphosed iron-rich skarn zones, often embedded in magnetite-rich rock. In contrast, andradite garnets from Marmoraton are known for their trapezohedral crystal habit, with layered and intergrown formations that range from honey-brown to greenish tones. These garnets crystallized in the contact zones between limestone and intrusive igneous rocks, where intense heat and fluid activity fostered their development. Collectors prize these specimens for their aesthetic appeal. The mine is long closed and mineral collecting is prohibited.