THE MINERAL ILVAITE

Chemistry: CaFe3OSi2O7(OH), Calcium Iron Silicate Hydroxide.
Class: Silicates
Subclass: Sorosilicates
Uses: mineral specimens
Specimens

Ilvaite is not a common mineral in rock shops. Its crystals are usually not all that attractive, but some specimens are real standouts with well-formed crystals with a shiny black color and an opaque submetallic luster. Its diamond-shaped crystals with wedge-like terminations can form very interesting specimens. Ilvaite is a member of the Sorosilicate subclass of the silicate minerals. Sorosilicates have an unusual basic unit of Si2O7. This group of atoms is composed of two silicate tetrahedrons that share one oxygen giving the group an hourglass shape. A fine specimen of ilvaite can be a valuable addition to anyones collection.

PHYSICAL CHARACTERISTICS:

Color is normally black, but also brownish black to dark gray.
Luster is submetallic or resinous.
Transparency crystals are opaque.
Crystal System orthorhombic; 2/m 2/m 2/m
Crystal Habits include elongated crystals with an overall diamond-shaped cross-section and wedge-shaped terminations. Also as platy crystals and in massive, compact and columnar specimens.
Cleavage very poor, in one direction lengthwise.
Fracture is conchoidal.
Hardness is 5.5 - 6
Specific Gravity is 3.8 - 4.1
Streak is brownish black.
Associated Minerals are arsenopyrite, stilbite, hematite, magnetite and pyrite.
Other Characteristics: crystals are usually striated lengthwise.
Notable Occurances Rio Marina, Elba, Italy; Serifos, Greece; Idaho and Greenland.
Best Field Indicators crystal habit, color, hardness, cleavage and localities.