Cahnite Locality: Franklin Mine , Franklin , Franklin Mining District, Sussex County, New Jersey , USA ( Locality at mindat.org ) Size: thumbnail, 1 x 0.8 x 0.5 cm Cahnite twin (found in 1921) This is a Cahnite, an extremely rar mineral even by Franklin standards, found just once in gem crystal quality in a small pocket in 1921 by a collector named Stanton. This one is even more rare, it is complexly twinned. However, the pics are tough and the piece is clear and difficult to shoot - suffice to say its better by far in person. This piece went to Harvard, and then it was exchanged to Dr. Mark Feinglos at some point. It has resided since in his collection for many years. These come to market only in recycled collections of ultimate rarities, and are so few and far between that most of us are lucky to even see one go by. It is pretty small by some standards; but relatively speaking though it is a giant of a piece for what it is. It is of a size that the twinning is readily visible to the eye, in person. Again, trust me, the piece is much better than the photo indicates. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Cahnite
A brittle, colorless tetragonal mineral with perfect cleavage and a hardness of 3.
Intro adapted from Wikipedia (CC BY-SA).
Cahnite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Ca₂B(AsO₄)(OH)₄.
It crystallizes in the tetragonal crystal system (space group I-4). It is a member of the Zircon structural group.
Key properties: Mohs hardness 3; specific gravity 3.156; Vitreous luster; optically uniaxial.
IMA symbol Cah, grandfathered status — known before the IMA’s founding, named in 1927.
A late-stage mineral in pegmatites cutting a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA); with zeolites in leucitic lava (Capo di Bove, Italy).
It is found associated with Hedyphane, friedelite, pyrochroite, franklinite, willemite, rhodonite, datolite, axinite, jarosewichite, samfowlerite, flinkite, hodgkinsonite, hetaerolite.
The mineral was named to honor Lazard Cahn (1865–1940), mineral collector and dealer, Colorado Springs, Colorado, USA, who first noted the species.