Iceland spar
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Description
Crystalline clear Calcite (calcium carbonate). Iceland spar has been commercially mined from the east coast of Iceland since the 17th century. Its double refraction and perfect cleavage was described by E.Bartholin in 1669. Because of its refracting ability, Iceland spar is used in polarizers (Nicol and Ahrens prisms), polarizing microscopes, and other optical instruments.
Synonyms and Related Terms
Iceland crystal; calcite; espato de Islandia (Esp.); espato de Islândia (Port.); Islandspat (Deut.)
Physical and Chemical Properties
- Trigonal crystal system with granular, stalatitic, massive or rhombohedral crystals
- Perfect cleavage in three directions
- Fracture = conchoidal
- Luster = vitreous to pearly
- Streak = white
- Can doubly refract light
- Fluorescence = aged surfaces of calcite may fluoresce purple or blue in ultraviolet light; freshly cleaved surfaces are white to yellow; may be phosphorescent
- Reacts with acids to evolve carbon dioxide
| Composition | CaCO3 |
|---|---|
| Mohs Hardness | 3.0 |
| Density | 2.71-2.72 g/ml |
| Refractive Index | 1.486; 1.658; (1.566) |
| Birefringence | 0.154 - 0.174 (very high) |
Resources and Citations
- G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 131
- Gem Identification Lab Manual, Gemological Institute of America, 2016.
- Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
- Wikipedia: Calcite (Accessed Sept 2 2005 and Dec 2022) hardness = 3, sp = 2.7
- Susan E. Schur, Conservation Terminology: A review of Past & Current Nomenclature of Materials, Technology and Conservation, Spring (p.34-39); Summer (p.35-38); Fall (p.25-36), 1985
- Jack Odgen, Jewellery of the Ancient World, Rizzoli International Publications Inc., New York City, 1982
- 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
- Encyclopedia Britannica, http://www.britannica.com Comment: "Iceland Spar." Accessed 25 Apr. 2004.