Ilvaite is a fairly common mineral but rarely discovered as being a gem that is faceted. Some of the mineral specimens are very collectable well-formed, shiny black, diamond-shaped crystals with sub-metallic luster. Gems are opaque black for collectors of the “black gem” category.
Ilvaite is bought at many locations worldwide including Elba, at Rio Marina and Capo Calamita; on Mt. Mulatto, near Predazzo, Trentino-Alto Adige, Italy. Very large crystals from Seriphos, Cyclades Islands, Greece; from the Kangerdluarssuk Plateau, in the Ilímaussaq intrusion, southern Greenland; fine crystals at Dal’negorsk, Primorskiy Kray, Russia; in america, very fine crystals from the Laxey mine, South Mountain, Owyhee County, Idaho; and the Prince of Wales Island, Alaska.
|Crystallography:||Orthorhombic – Dipyramidal|
|Crystal Habit:||Crystals prismatic, to 25 cm; columnar, radiating, or compact massive.|
|Cleavage:|| Distinct,  Distinct|
|Hardness (Mohs):||5.5 – 6.0|
|Density:||3.99 – 4.05 (g/cm3)|
|Color:||Iron Black, dark Grayish Black|
|Transparency:||Opaque; Translucent on thin edges|
|Refractive Index:||1.727 – 1.883 Biaxial ( + )|
|Dispersion:||Strong; r < v|
|Pleochroism:||Strong; X = dark green; Y = yellow-brown to dark brown; Z = dark brown|
|Anisotrophism:||Strong; color in reflected light: light gray to bluish gray, pinkish red to violet|