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Colorless crystals or white amorphous powder. Silica is widely available because it makes up one of the largest portions of the earth's crust. In its purest form, silica, or silicon dioxide, occurs as crystalline Quartz. The more common, but less pure, forms are Quartzite, Sandstone, Flint, Agate, and Sand. The fossil form of silica is Diatomaceous earth. All forms of silica are inert, unaffected by heat, insoluble in strong acids (except hydrofluoric) and slowly attacked by strong alkalis. Silica is not commonly used as a pigment, however, it is found in grounds, primers and wood fillers. Silica is used in the manufacture of glass, water glass, abrasives, ceramics and enamelware.

See also Fumed silica, and Silica gel.

Synonyms and Related Terms

silicon dioxide; silicic anhydride; quartz; silex; diatomaceous earth; flint; diatomite; sand; quartzite; sandstone; amethyst; jasper, chalcedony; agate; onyx; tridymite; opal; cristobalite; Pigment White 27; Siliziumdioxid (Deut.); Kieselgur (Deut.); Kieselerde (Deut.); silice (Fr., Esp., It.); chalazias (Gr.); kwarts (Ned.); sílica (Port.)


Noncombustible. Toxic by inhalation. Chronic exposure to dust may cause silicosis



Physical and Chemical Properties

  • Soluble in hydrofluoric acid.
  • Density (g/ml) = 2.2 (amorphous) and 2.65 (quartz).
Composition SiO2
Melting Point 1710 C
Boiling Point 2230 C


Properties of Common Abrasives

Characteristics of Common White Pigments

Resources and Citations

  • R. J. Gettens, G.L. Stout, Painting Materials, A Short Encyclopaedia, Dover Publications, New York, 1966
  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 708
  • Ralph Mayer, A Dictionary of Art Terms and Techniques, Harper and Row Publishers, New York, 1969 (also 1945 printing)
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Michael McCann, Artist Beware, Watson-Guptill Publications, New York City, 1979
  • Matt Roberts, Don Etherington, Bookbinding and the Conservation of Books: a Dictionary of Descriptive Terminology, U.S. Government Printing Office, Washington DC, 1982
  • Dictionary of Building Preservation, Ward Bucher, ed., John Wiley & Sons, Inc., New York City, 1996
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 8637
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998

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