Obsidian

Egyptian amulet
MFA# 57.521

Description

Obsidian

A dark,shiny glass formed in nature by the rapid cooling of lava. Obsidian is widely distributed and has been used since Paleolithic (before 3500 BCE) times for mirrors, weapons, tools, and jewelry. Sources of obsidian include Anatolia, Armenia, Ethiopia, Greece (Milos), Italy (Lipari, Eolie), Iceland, the U.S. (Wyoming), Mexico (Teotihuacan), Guatemala (Tikal), and Peru. Obsidian is often black in color but may also be yellow, red, brown or green. It produces conchoidal fractures when cleaved. Analysis of trace elements in obsidian pieces can be traced back to their original deposits. This has been used to evaluate early trading patterns.

Obsidian thin section

Synonyms and Related Terms

volcanic glass; basalt glass; tachylite; perlite; calite; mountain mahogany (deep red obsidian); Apache tears (pebble-like nodules); obsidian snowflake (black with white inclusions); obsidiana (Esp., Port.); obsidienne (Fr.); Obsidian (Deut.); obsidiaan (Ned.)

FTIR (MFA)

Physical and Chemical Properties

• Transparent to translucent
• Luster = vitreous
• Fluorescence = generally inert
• Pleochroism = usually none
• Birefringence = none
• Inclusions = possible gas bubbles, stubby needles; banding

Mohs Hardness	5 - 7
Density	2.4 g/ml
Refractive Index	1.482-1.496

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. 641
• Jack Odgen, Jewellery of the Ancient World, Rizzoli International Publications Inc., New York City, 1982
• Encyclopedia of Archaeology, Glyn E. Daniel, ed., Thomas Y. Crowell Co., New York, 1977
• A.Lucas, J.R.Harris, Ancient Egyptian Materials and Industries, Edward Arnold Publishers Ltd., London, 4th edition, 1962
• C.W.Chesterman, K.E.Lowe, Audubon Society Field Guide to North American Rocks and Minerals, Alfred A. Knopf, New York, 1979; Mohs hardness = 6-7
• Wikipedia: Obsidian (Accessed Nov. 9, 2005 and Dec 2022); Mohs hardness = 5-6
• George Savage, Art and Antique Restorer's Handbook, Rockliff Publishing Corp, London, 1954
• Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976
• Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
• The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
• CRC Handbook of Chemistry and Physics, Robert Weast (ed.), CRC Press, Boca Raton, Florida, v. 61, 1980; ref. index=1.482-1.496