Seashell

Conch shell trumpet
MFA 1988.1214

Description

A hard outer covering of a mollusk. Seashells are composed primarily of calcium carbonate (Aragonite) bound with chitin. Some seashells, such as Abalone, Pearl oyster and mussel, have a hard iridescent inner layer. The iridescence is caused by the interference of light waves reflected between the thin overlapping layers. Seashells are soft and easily cut or carved. They have been used for beads, amulets and decoration since ancient times in both Eastern and Western cultures.

Shell trumpet
MFA# 17.2170

Synonyms and Related Terms

sea shell; nacre (Fr.); oyster shells; concha marinha (port.);

FTIR (MFA)

Raman (MFA)

Chemical structure

Risks

• No significant hazards.
• ThermoFisher: SDS

Physical and Chemical Properties

• Reacts with acids to evolve carbon dioxide.
• Aragonite is harder and denser than calcite
• Fracture = uneven to splinter
• Luster = greasy or pearly
• Streak = white
• Fluorescence = variable
• Birefringence = strong (0.155) showing interference colors (for mollusk shells)
• Straight extinction

Mohs Hardness	3.5 - 4.0
Density	2.93-2.95 g/ml
Refractive Index	1.530 - 1.686

Resources and Citations

• Gem Identification Lab Manual, Gemological Institute of America, 2016.
• Wikipedia: Seashell Accessed Dec 2022.
• Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
• Oppi Untracht, Jewelry Concepts and Technology, Doubleday & Co., Inc., New York City, 1985
• Jack Odgen, Jewellery of the Ancient World, Rizzoli International Publications Inc., New York City, 1982
• 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