2" Andradite Garnets on Hedenbergite - Greece

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.

Hedenbergite is a calcium iron (magnesium) silicate that often bears a range of green to brown coloration. The crystals are typically opaque and occur in stubby or prismatic aggregates. Inner Mongolia, Russia, and Greece all produce quartz crystals colored green by fibrous hedenbergite inclusions. A variety of hedenbergite can be found in Sweden as well: green-black, blocky crystals come from the Nordmark Odal Field in Värmland County.

Hedenbergite was given its name in 1819 by Jöns Jakob Berzelius, a Swedish chemist. He named the mineral in honor of Anders Ludvig Hedenberg, a chemistry student and co-worker who originally discovered and described the mineral in Tunaberg, Sweden.

The general chemical formula of Hedenbergite is CaFe2+Si2O6 .