Forsterite var Peridot

Formula: Mg2SiO4

Colour: Green, pale yellow or white.

Lustre: Vitreous

Hardness: 7

Specific Gravity: 3.275

Crystal System: Orthorhombic

Member of: Olivine Group

Known in ancient times and some smaragdus and beryllos (Pliny, 79) may have been what is now called forsterite. (N.B. The “chrysolithas” of Pliny (79) is believed to be topaz.) The earliest name given to an undisputed olivine group species was chrysolit (chrysolite) and was named by Johan Gottschalk Wallerius in 1747, although the name chrysolite was later used by Balthasar Georges Sage in 1777 for what is now known as prehnite. In 1755, Antoine Joseph Dezallier d’Argenville called this species “peridot ordinaire”, while Axel Cronstedt named it “gulgron topas” in 1758. In 1772, Rome d’Lisle renamed the mineral “chrysolite ordinaire”. Wallerius’s chrysolite was renamed, olivine, in 1789 by Abraham Gottlieb Werner for the usual olive green color of this mineral (N.B. chrysolite has a similar etymology.) Friedrich Walchner in 1823 gave it the name “hyalosiderite”. Named forsterite in 1824 by Serve-Dieu Abailard “Armand” Lévy in honor of Adolarius Jacob Forster [April 6, 1739, Grossbreitenbach, Thuringia, Germany – May 1806 St. Petersburg, Russia], German mineral collector and mineral dealer, who variously resided in England and Russia. Boltonite was introduced in 1835 by Charles Upham Shepard, while glinkit was named in 1847 by Romanovski.

Type Locality: Mount Somma, Somma-Vesuvius Complex, Naples, Campania, Italy

Polymorph of: Poirierite, Ringwoodite, Wadsleyite

Olivine Group. Fayalite-Forsterite Series, and the Forsterite-Tephroite Series.
The magnesium analogue of Fayalite, Tephroite, and Calcio-Olivine.

 Name: Peridot is a gem-quality Olivine.  The origin of the name peridot is uncertain. The Oxford English Dictionary suggests an alteration of Anglo–Norman pedoretés (classical Latin pæderot-), a kind of opal, rather than the Arabic word faridat, meaning “gem”. (From Wikipedia).

A variety of Forsterite. A green gem variety of Forsterite.