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Calcium Feldspar

Calcium rich feldspars are termed ´anorthites´. Where calcium feldspar is the predominant rock-forming mineral, the rock is termed ´anorthosite´.  Deposits of anorthosite are unusual.

Feldspar is the name of a group of rock-forming minerals which make up as much as 60% of the Earth´s crust. Feldspars crystalize from mamga in both intrusive and extrusive igneous rocks, and they can also occur as compact minerals, as veins, and are also present in many types of metamorphic rocks.  A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure and specific physical properties. Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known forms. A rock, by comparison, is an aggregate of minerals and as such, need not have a specific chemical composition.

The physical characteristics of calcium feldspars are generally:

  1. Color - Usually white, gray or colorless but can be pale shades of other colors.
  2. Luster - Vitreous to dull if weathered.
  3. Transparency - Crystals are translucent to opaque and only sometimes transparent


Calcium feldspar has an application as a raw material in certain glass and ceramic applications; notably certain types of fiberglass and ceramic tile formulations. Other potential applications include:

  • Refractive linings in aluminum reduction cells
  • Raw material for rock wool manufacture
  • Filler for certain molding compounds and specialty paper products
  • Slag conditioner in ferrosilicon and silicon metal manufacture, and
  • Dimension or ornamental stone

Calcium feldspar, as a component of batch feed, have demonstrated that acceptable quality glass and ceramic products can be produced, with the fundamentally important advantages of lowering the melting temperature and energy demand of the glass batch, thereby reducing energy intensity and carbon footprint. 

Bundle Of Fibreglass

Bundle of fiberglass
Inside A Glass Melting Furnace


Avalon´s Activities
Avalon is currently developing one such deposit in Warren Township, in Northern Ontario for use in the glass and ceramics industry. The processing of the anorthosite is relatively simple - the rock is mined, crushed, put through a magnetic separation process to remove iron impurities, and further ground before it is fed into glass furnaces. The calcium feldspar is a principle source of three components for the glass melt: calcium, aluminum, and silica. Full scale trials have been conducted in an operating fibreglass production furnace.