Danalite Locality: Rockport , Essex County, Massachusetts , USA ( Locality at mindat.org ) Size: 7.2 x 4.8 x 3.2 cm. From the TYPE LOCALITY where it was first noted in 1866 during the Civil War, this is a superb, intensely colored danalite crystal, named after the great mineralogist. The crystal is approx. 2 cm tall. Danalite turns out to be a rare member of the helvite group, seldom crystallizing and most often found as masses in rock. Here we have a superb 3-dimensional crystal perched on matrix with amazonite feldspar and cryophilite, in quartz. According to MINDAT, cryophilite has been discredited by the IMA Mica subcommittee. It is now considered an odd variety of Zinnwaldite, Fe-bearing trilithionite, or Fe-bearing polylithionite (again, according to MINDAT). Ex. Academy of Natural Sciences Philadelphia Collection. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Danalite
A rare iron-beryllium silicate-sulfide of the helvine group found in granites, pegmatites and skarns.
Intro adapted from Wikipedia (CC BY-SA).
Danalite is an IMA-recognized mineral species in the silicate class, with the chemical formula Be₃Fe²⁺₄(SiO₄)₃S.
It crystallizes in the cubic crystal system (space group P-43n). It is a member of the Cancrinite-sodalite, Sodalite structural group.
Key properties: Mohs hardness 5.5–6; specific gravity 3.28–3.46; Vitreous or greasy luster; refractive index 1.759; optically isotropic.
IMA symbol Dan, grandfathered status — known before the IMA’s founding, named in 1866.
Found in granites, granite pegmatites, zones of contact metamorphism, skarns, and gneisses.
It is found associated with Magnetite, garnet, fluorite (skarn); albite, cassiterite, pyrite, muscovite (tin-bearing pegmatites); arsenopyrite, quartz, chlorite (hydrothermal deposits).
The mineral was named to honor James Dwight Dana (1813–1895), American geologist and mineralogist, Yale University, New Haven, Connecticut, USA.