Is a Calcium Iron Silicate Hydroxide with formula: CaFe3OSi2O7(OH),
The hardness is 5.5-6. It’s name comes from Ilva, an ancient name given to Elba island where has been found for the first time. The color is usual black oR brownish and opaque.Is not a common mineral and now very difficult to find in this location.This piece comes from my collection .
From Rio Marina, Elba island, Italy