Peridot
| Peridot | |
|---|---|
 |
|
| General | |
| Category | Silicate mineral variety |
|
Formula (repeating unit) |
(Mg, Fe)2SiO4 |
| Crystal system | Orthorhombic |
| Identification | |
| Color | Yellow, to yellow-green, olive-green, to brownish, sometimes a lime-green, to emerald-ish hue |
| Cleavage | Poor |
| Fracture | Conchoidal |
| Mohs scale hardness | 6.5–7 |
| Luster | Vitreous (glassy) |
| Streak | None |
| Specific gravity | 3.2–4.3 |
| Refractive index | 1.64–1.70 |
| Birefringence | +0.036 |
Peridot (/ˈpɛrᵻdɒt/ or /ˈpɛrᵻdoʊ/) is gem-quality olivine, which is a silicate mineral with the formula of (Mg, Fe)2SiO4. As peridot is the magnesium-rich variety of olivine (forsterite), the formula approaches Mg2SiO4.
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".
The Middle English Dictionary's entry on peridot includes several variations : peridod, peritot, pelidod and pilidod – other variants substitute y for the is seen here.
The earliest use in England is in the register of the St Albans Abbey, in Latin, and its translation in 1705 is possibly the first use of "peridot" in English. It records that on his death in 1245, Bishop John bequeathed various items including peridot to the Abbey.
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 the percentage of iron that is contained in the crystal structure, so the color of individual peridot gems can vary from yellow, to olive, to brownish-green. In rare cases, peridot may occur in a medium-dark toned, visually pure green with no secondary yellow hue or brown mask.
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