Polished Optical Calcite Slabs

Slab of birefringent (doubly refracting) transparent optical calcite from Brazil. Polished to beautiful shimmer, they come in irregular shapes and sizes, ranging between 1 and 3 inches (2.5 to 7.5 cm) cubed. Some are clear and some have translucent imperfections.

Features:

• High-quality, polished optical calcite
• Some varieties are utilized for optical purposes
• Elegant and unique gift idea

Note: Please, be aware that this is a natural mineral and as such each piece is one of a kind! The one you receive may not be exactly the same as those pictured but it will be similar.  Price is per each piece.

ABOUT OPTICAL CALCITE:

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It has a Mohs hardness of 3, a specific gravity of 2.71, and its luster is vitreous in crystallized varieties. Calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence. A transparent variety called Iceland spar is used for optical purposes.

Single calcite crystals display an optical property called birefringence (double refraction). This strong birefringence causes objects viewed through a clear piece of calcite to appear doubled. The birefringent effect (using calcite) was first described by the Danish scientist Rasmus Bartholin in 1669. At a wavelength of ~590 nm calcite has ordinary and extraordinary refractive indices of 1.658 and 1.486, respectively. Between 190 and 1700 nm, the ordinary refractive index varies roughly between 1.6 and 1.4, while the extraordinary refractive index varies between 1.9 and 1.5.

Calcite, like most carbonates, will dissolve with most forms of acid. Calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, and dissolved ion concentrations. Although calcite is fairly insoluble in cold water, acidity can cause dissolution of calcite and release of carbon dioxide gas. Calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases.

Calcite is often the primary constituent of the shells of marine organisms, e.g., plankton (such as coccoliths and planktic foraminifera), the hard parts of red algae, some sponges, brachiopoda, echinoderms, most bryozoa, and parts of the shells of some bivalves, such as oysters and rudists).

Calcite is a common constituent of sedimentary rocks, limestone in particular, much of which is formed from the shells of dead marine organisms. Approximately 10% of sedimentary rock is limestone.

Calcite is the primary mineral in metamorphic marble. It also occurs as a vein mineral in deposits from hot springs, and it occurs in caverns as stalactites and stalagmites.

Calcite may also be found in volcanic or mantle-derived rocks such as carbonatites, kimberlites, or rarely in peridotites.

Calcite is found in spectacular form in the Snowy River Cave of New Mexico as mentioned above, where microorganisms are credited with natural formations.

Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes.