The origin of the name "peridot" is uncertain. The Oxford English Dictionary suggests an alteration of Anglo–Normanpedoretés (classical Latinpæderot-), a kind of opal, rather than the Arabic word faridat, meaning "gem".
Peridot is the transparent gem variety of the mineral olivine.
Peridot is one of the few gemstones that occur in only one color, an olive green. The intensity and tint of the green, however, depends on how much iron is contained in the crystal structure, so the color of individual peridot gems can vary from yellow- to olive- to brownish-green. The most prized of peridot is dark olive-green colour.
However,the largest faceted peridot olivine is a 310 carat specimen in the Smithsonian Museum in Washington, D.C.
Chemical
(Mg, Fe)2SiO4, with Mg in greater quantities than Fe.
Magnesium iron silicate.
composition
Peridot is a member of an isomorphous series with forsterite (magnesium
silicate) and fayalite (iron silicate) as 'end members' of this olivine series.
Crystal system
Orthorhombic.
Cleavage
Poor.
Hardness
6.5 – 7 on moh’s scale
Specific gravity
3.32 to 3.37
Colour
Pale yellowish-green to deep green, greenish-brown to brown (rare).
Pleochroism
Weak, green and yellowish-green.
Lustre
Vitreous, sometimes appears oily.
Refractive index
1.65 to 1.69
Birefringence
0.036 Inclusions and facet edges may appear doubled through the 10x lens.
Dispersion
Medium.
Optical nature
Biaxial.
Inclusions
Black chromite crystals which induce flat stress cracks -
these resemble water-lily leaves. Mica flakes - these
may give the stone a slightly brownish hue.
In larger stones inclusions appear doubled due to the
large double refraction.
Localities
Main sources of gem material include China, Myanmar (Mogok district),
Pakistan, USA (Arizona) and Zabargad (S1, John's Island) in the Red Sea.
