This Specimen has been sold.
4.05" Lustrous Marcasite Crystals on Calcite - Linwood Mine, Iowa
This is a beautiful, 4.05" wide specimen of lustrous marcasite crystals on calcite that was collected from the Linwood Mine in Buffalo, Iowa. Comes with an acrylic display stand.
The Linwood Mine has been in operation since 1944 and to this day, ranks as one of the largest limestone mining locations in the United States. On relatively rare occasions, a vug will be opened in the mining process, in which the minerals contained within this vug are extracted and saved. These vugs often contain beautiful crystal aggregations of calcite, barite, and marcasite, some of which are considered world-class quality specimens.
Marcasite is an iron sulfide mineral with the chemical formula FeS2. It is similar to pyrite in both its chemical composition and appearance, however it forms with a different crystal structure and is much more reactive to humidity. It is often found within sedimentary rock and hydrothermal deposits, and at one point was used for its sulfur content.
Calcite, CaCO3, is a carbonate mineral and the most stable polymorph of calcium carbonate. The other polymorphs are the minerals aragonite and vaterite. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals. However, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, and prisms. Calcite exhibits several twinning types adding to the variety of observed forms. It may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form.