Petedunnite Locality: Franklin, Franklin Mining District, Sussex County, New Jersey, USA Dimensions: 8 cm x 7 cm x 3.5 cm; weight: 225 g Gift of John Cianciulli (June 2000). MOB coll. The petedunnite is the dark green stuff on top. It looks much like any other dark green pyroxene to me so I don't think it would be possible to ID the stuff visually. Presumably John had good provenance on this specimen. According to Dunn's Franklin/Sterling Hill monograph, petedunnite has one poor cleavage on {110}. In this specimen, cleavage (or parting) seems evident from a distance but appears very indistinct under a scope. (This is from the Buckwheat Dump but I don't know if it has been established that petedunnite is actually from the Buckwheat pit. Hence I posted under the more generic "Franklin Mine".) — Photo: Modris Baum · Public domain
Petedunnite
Petedunnite is an IMA-recognized mineral species in the silicate class, with the chemical formula CaZnSi₂O₆.
It crystallizes in the monoclinic crystal system (space group C2/c). It is a member of the Pyroxene structural group.
Key properties: specific gravity 3.68; Vitreous luster; optically biaxial.
IMA symbol Pdu, IMA status: approved, named in 1983.
Found in a metamorphosed stratiform zinc deposit, apparently formed under relatively high activity of sulfur and oxygen. Formed at high pressures (P > 0.8 GPa); at lower pressures and temperatures (>650 flC) decomposes to willemite.
It is found associated with Calcite, gahnite, willemite, genthelvite, garnet, albite, sphalerite.
In honor of Dr. Pete J. Dunn, Department of Mineral Sciences (1984-2007), Smithsonian Institution, Washington, D.C., USA, for contributions to the mineralogy of Franklin and Sterling Hill.