Phenacite or Phenakite is a nesosilicate mineral with beryllium orthosilicate content. It has a chemical formula Be2SiO4. This mineral forms rhombohedral crystals that have a hemihedrism of the parallel - face, in an isolated crystal configuration, and follows a prismatic or lenticular habit. The factors that determine the lenticular habit are the appearance of obtuse rhombohedra with several faces without the prism face. This mineral has a conchodial fracture and has no cleavage. Many confuse this mineral with quartz for similarity in looks.
Derivation of Name
It gets its name from the Greek word phenakos - "deceiver", referring to its visual likeness to Quartz.
Occurrence and Source
Phenakite occurs in high-temperature pegmatite veins and mica-schists coupled with Quartz, Apatite, Chrysoberyl and Topaz. Since long it has been realized from the emerald and chrysoberyl mine on the Takovaya stream, close to Yekaterinburg in the Urals of Russia, where big crystals are found in mica-schist. It also occurs with amazon-stone and topaz in the Pikes Peak region in Colorado (USA) and granite of the Ilmen Mountains in the southern Urals. Big crystals having prismatic pattern have been located in a Feldspar quarry at Kragero in Norway. Framont near Schirmeck in Alsace, in the French Northeast is one more renowned locality. Still bigger crystals, of 1 to 2 in. diameter and weighing 28 lb have been located at Greenwood in Maine, but these are pseudomorphs of quartz after phenakite.
Sometimes used as a gemstone
Phenakite is an uncommon beryllium mineral, found in pegmatitic pockets and is linked to gemstones like Beryl, Topaz, particularly Emerald, Smoky Quartz and Chrysoberyl. Phenakite is among the few silicate minerals with trigonal symmetry. This symmetry is a lot more widespread among carbonates than among silicates. It has the same symmetry as the emerald green silicate Dioptase and the glowing and closely associated Willemite.
The crystals are occasionally flawlessly colorless and transparent, but more frequently they are yellowish or grayish and only semi-transparent, rarely they are pale rose-red.
7.5 - 8