mineral

Optical Calcite (Iceland Spar)

Calcite (Calcium Carbonate, CaCO3)

Hardness: 3 on Mohs scale; Color: Clear to pale yellow/honey; Luster: Vitreous to pearly; Crystal structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral in three directions; Specific gravity: 2.71

Hardness: 3 on Mohs scale
Color: Clear to pale yellow/honey
Luster: Vitreous to pearly

Identified April 10, 2026More mineral →

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Physical properties

Formation & geological history

Formed through precipitation from calcium-rich hydrothermal solutions or within sedimentary environments like limestone caverns. It can form in various geological ages ranging from Precambrian to recent.

Uses & applications

Primary source of lime for cement, used in optical instruments (polarizing microscopes), soil treatment, and highly popular for metaphysical/mineral collecting.

Geological facts

Iceland Spar was first thoroughly described in the 17th century. It exhibits double refraction (birefringence), meaning if you place it over a line, you will see two lines. Vikings may have used it as a 'sunstone' for navigation.

Field identification & locations

Identify by its rhombohedral shape (like a slanted cube), its softness (can be scratched by a copper penny), and its reaction to dilute hydrochloric acid (it will fizz). Found globally, with notable deposits in Iceland, Mexico, and the USA.

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