Tiny black crystal of the extremely rare Lengenbach minerals stalderite-ralphcannonite (this one, new species: IMA 2014-077) in a small matrix of realgar. Stalderite and ralphcannonite form a series, where stalderite is the Cu-end member and ralphcannonite is the Ag-end member. This crystal was analyzed by EDX and it is stalderite (61%) and ralphcannonite (39%). In addition, this specimen is a part of the type specimen of ralphcannonite (!), that is, the specimen that was used for the description of the species! Only very few specimens known of both species. After the book "Faszination Lengenbach (2008)" we know that the total number of stalderite specimens known was only 9! Specimen found in 1989. — Photo: David Hospital · CC BY-SA 4.0
Ralphcannonite
Ralphcannonite is an IMA-recognized mineral species in the sulfosalt class, with the chemical formula AgZn₂TlAs₂S₆.
It crystallizes in the tetragonal crystal system (space group I-42m). It is a member of the Routhierite structural group.
Key properties: Mohs hardness 2–2.5; specific gravity 4.927; Black streak; Metallic luster.
IMA symbol Rcn, IMA status: approved, named in 2014.
Found in massive to interstitial sulfosalt accumulations in metamorphosed (upper greenschist to amphibolite facies) dolostone.
It is found associated with Dufrénoysite, hatchite, realgar, baryte.
The mineral was named to honor Ralph Cannon (b. 1956) for his contributions to the mineralogy of the Lengenbach quarry.