Fermorite is a mineral that belongs to the amphibole group. It is specifically classified as a sodium- and manganese-rich variety of the mineral grunerite. The name "fermorite" is derived from the British petrologist and geologist, Dr. Louis Leigh Fermor, who first identified and described this mineral in the early 20th century.
Fermorite typically occurs as brownish-black prismatic crystals or in fibrous or columnar aggregates. It has a vitreous to silky luster, with a Mohs hardness ranging from 5 to 6. The mineral displays perfect cleavage along two directions, and its streak is light brown. Fermorite is commonly found in metamorphic rocks that have undergone regional or contact metamorphism, and it is often associated with minerals such as quartz, feldspar, garnet, and biotite.
In terms of its chemical composition, fermorite is primarily composed of sodium, manganese, iron, silicon, and oxygen, with smaller amounts of aluminum and other trace elements. Its specific gravity typically ranges around 3.4 to 3.7. Fermorite is known for its refractive index, which is higher than that of most amphiboles.
Due to its distinctive properties, fermorite can be identified using various analytical techniques, including X-ray diffraction, electron microscopy, and microprobe analysis. Its unique crystal structure and chemical composition make fermorite an important mineral for geological and mineralogical studies. Furthermore, fermorite has no significant economic importance and is primarily valued for its scientific and aesthetic value.
