Collection: Optical calcite

Optical calcite , also called Iceland spar , is a transparent and pure variety of calcite (calcium carbonate, CaCO₃). It is famous for its exceptional optical properties , notably the phenomenon of birefringence , which makes it a widely used material in optics and mineralogy.

🌟 Main Features

Chemical formula : CaCO₃
Crystal system : Rhombohedral (trigonal)
Hardness (Mohs scale) : 3
Cleavage : Perfect in three directions (rhombohedral)
Color : Colorless to white in its pure form (optical calcite is usually clear)
Transparency : Transparent to translucent
Birefringence : Very strong (δ ≈ 0.172)

🔍 Birefringence phenomenon

Optical calcite is one of the best examples of birefringence (or double refraction):

When a light ray enters the crystal, it is split into two polarized rays that follow slightly different paths.
Looking at an object through an optical calcite crystal, one sees a doubled image .

This phenomenon is linked to the anisotropic crystal structure of calcite, which causes light to propagate at different speeds depending on the direction.

🧪 Applications

Optical prisms and polarizers (such as Nicol polarizers)
Polarizing microscopy studies
Experiments in light physics
Collectibles (in mineralogy)

📍 Origin and deposits

Iceland spar gets its name from its abundance in Iceland , but it is also found in:

Mexico
The United States
China
Norway

The most prized crystals are clear, without inclusions, and cut to precise angles for optical uses.

✨ Interesting Facts

Isaac Newton and other pioneers of optics studied optical calcite as early as the 17th century.
It is a perfect example of an anisotropic mineral in mineralogy and crystallography courses.