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Layered onyx
MFA# 99.101


A variety of Agate that has parallel, alternating bands of Chalcedony and Opal. The bands are usually colored black/white or red/white. In ancient times, the stones were available in Egypt, Arabia, and India. Onyx was often used as a gemstone in the production of cameos and intaglios. Onyx is also used as an ornamental building stone and for decorative items such as table tops, lamp bases, and small boxes. It was popularly used for geometric patterns in Art Deco designs of the 1920s. Limestone onyx, also called onyx marble, dark layers of impurities and polishes to a high gloss. Mexican onyx is a banded limestone made from stalactites. Argentine onyx is a dark-green stone. Sardonyx has layers of Sard (brownish) alternating with lighter-color layers of Carnelian (red).

Onyx brooch
MFA# 53.79

Synonyms and Related Terms

agate; onyx marble; sardonyx; Mexican onyx; Onyx (Deut.); ónice (Esp.); onyx(Fr.); onyks (Pol.); onix (Port.); onyx (Ned.)


Inhalation of dust may be toxic resulting in silicosis.

Physical and Chemical Properties

  • Composition = SiO2
  • No visible crystals
  • Fracture = conchoidal, uneven, splintery
  • Luster = waxy to vitreous
  • Streak = white
  • Fluorescence = generally inert
  • Pleochroism = absent
  • Mohs Hardness = 6.5 - 7.0
  • Density = 2.6
  • Refractive Index = 1.530 - 1.543
  • Birefringence = 0.004 - 0.009


Properties of Common Gemstones

Resources and Citations

  • Gem Identification Lab Manual, Gemological Institute of America, 2016.
  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 565
  • Ralph Mayer, A Dictionary of Art Terms and Techniques, Harper and Row Publishers, New York, 1969 (also 1945 printing)
  • Jack Odgen, Jewellery of the Ancient World, Rizzoli International Publications Inc., New York City, 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
  • A.Lucas, J.R.Harris, Ancient Egyptian Materials and Industries, Edward Arnold Publishers Ltd., London, 4th edition, 1962
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • Website: http://www.marble-institute.com
  • Wikipedia: Onyx varieties (Accessed Sept. 14, 2005 and Dec 2022)
  • Michael McCann, Artist Beware, Watson-Guptill Publications, New York City, 1979
  • Tom Rowland, Noel Riley, A-Z Guide to Cleaning, Conserving and Repairing Antiques, Constable and Co., Ltd., London, 1981