3" Rainbow Andradite Garnets with Calcite - Norway

Rainbow Andradite Garnets with Calcite - Norway #342363

This is a beautiful cluster of iridescent andradite garnets mined at Fem-minutter'n in Buskerud, Norway. The iridescence of these garnets is naturally occurring and can be attributed to two different types of lamellar structures. These lamellar structures cause predominantly thin-film interference and most likely diffraction of light.

A paper on this natural iridescent phenomenon in andradite garnets is linked below.
The Cause of Iridescence in Rainbow Andradite From Nara, Japan

The specimen measures 3" wide and is accompanied by a small acrylic display stand.

Andradite is a species of the garnet group, and although not as well-known as some other types of garnets, such as Almandine or pyrope, it is the most lustrous. It tends to be opaque, so most andradite is not gemstone-quality. It occurs in skarns developed in contact-metamorphosed impure limestones or calcic igneous rocks; in chlorite schists and serpentinites; and in alkalic igneous rocks, often titaniferous.

Andradite comes in three varieties: melanite, colored by titanium substitutions for iron in its formula; topazolite, a rare and yellow-green variety; and demantoid, a striking green variety that is one of the world's rarest and most valuable gemstones.

Garnets are nesosilicates with the general formula X3Y2(SiO4)3. There are many species of garnet, including pyrope, almandine, spessartine, uvarovite, andradite, and grossular (varieties of which are hessonite, cinnamon-stone and tsavorite). Garnets are found in a wide variety of colors including red, orange, yellow, green, purple, brown, blue, black, pink, and colorless, though reddish shades are the most common.

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