A cube of Iceland spar.
Iceland spar definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
a transparent, colorless calcite, found esp. in Iceland: it is used by opticians for making double-refracting prisms
Iceland spar definition by American Heritage Dictionary
nounThe American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
A doubly refracting transparent calcite used in optical instruments.
iceland spar - Science Definition
A form of calcite that is transparent and causes light passing through it to refract in two directions (forming a double image of an object seen through it). Iceland spar occurs in perfect rhombohedrons and is used in optical instruments.