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THE MINERAL ILVAITE


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 Si 2 O 7 . 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.

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