AndraditeAndradite is a mineral species of the garnet group. It is a nesosilicate, with formula Ca3Fe2Si3O12. Andradite includes three varieties: Melanite: Black in color, referred to as "titanian andradite". Demantoid: Vivid green in color, one of the most valuable and rare stones in the gemological world. Topazolite: Yellow-green in color and sometimes of high enough quality to be cut into a faceted gemstone, it is rarer than demantoid. It was first described in 1868 for an occurrence in Drammen, Buskerud, Norway.
HornblendeHornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rocks. The general formula is . Hornblende has a hardness of 5–6, a specific gravity of 3.0 to 3.6, and is typically an opaque green, dark green, brown, or black color. It tends to form slender prismatic to bladed crystals, diamond-shaped in cross-section, or is present as irregular grains or fibrous masses.
Mineral hydrationIn inorganic chemistry, mineral hydration is a reaction which adds water to the crystal structure of a mineral, usually creating a new mineral, commonly called a hydrate. In geological terms, the process of mineral hydration is known as retrograde alteration and is a process occurring in retrograde metamorphism. It commonly accompanies metasomatism and is often a feature of wall rock alteration around ore bodies. Hydration of minerals occurs generally in concert with hydrothermal circulation which may be driven by tectonic or igneous activity.
