Yellow sassolite from Vulcano island, Italy . Photograph taken at the Natural History Museum , London . — Photo: Aram Dulyan ( User:Aramgutang ) · Public domain
Sassolite
Natural boric acid — white-to-gray crusts and scales deposited in volcanic fumaroles and hot springs.
Intro adapted from Wikipedia (CC BY-SA).
Sassolite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula B(OH)₃.
It crystallizes in the triclinic crystal system (space group P-1).
Key properties: Mohs hardness 1; specific gravity 1.46–1.5; Pearly luster; refractive index 1.418; optically biaxial.
IMA symbol Sso, grandfathered status — known before the IMA’s founding, named in 1800.
An evaporite or sublimate around hot spring lagoons and volcanic fumaroles; in bedded sedimentary borate deposits.
It is found associated with Larderellite, santite, ginorite, probertite, searlesite, mirabilite, hieratite, glauberite, sulfur, realgar, sal ammoniac, alums.
The name refers to its initially-noted occurrence at Sasso, Italy.