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Introduction:
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Peridot, the August birthstone, is relatively familiar to consumers but can sometimes be confused with a wide variety of green stones. Peridot demonstrates a unique double refraction, which is very helpful in identifying the stone. The mineralogical word to describe peridot is olivine and it occurs in a series of minerals with forsterite and fayalite on opposite ends of the series. Peridot is a somewhat delicate stone that may burst and/or fracture under pressure or high heat. It is also reactive to sulfuric and hydrochloric acids. Some people with acidic perspiration will notice an effect on peridot jewelry over time. Sources for peridot include Australia, Brazil, China, Kenya, Mexico, Pakistan, Sri Lanka, South Africa, Tanzania, and Arizona. |
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History
of...
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The name peridot is derived from Greek, but its meaning is unclear. The stone has enjoyed popularity throughout history, especially during the baroque period. It was brought to Central Europe by crusaders and was frequently used for ecclesiastical purposes. Today Native Americans prize the stone as one of their most popular gems. Peridot is typically cut in the step and table fashions, but some stones are brilliant cut. History's most acclaimed deposit of peridot is Zebirget, an island in the Red Sea that is 188 miles east of Aswan, Egypt. The deposit was mined for over 3500 years, abandoned, and then rediscovered around 1900. The largest cut peridot was found on Zebirget. It weighs 310 carats and is housed in the Smithsonian Institute.
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Technical
Specifications:
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| DESCRIPTION |
| Peridot is a member of the forsterite-fayalite mineral series. |
| Chemical
Composition: |
(Mg, Fe)2SiO4 |
| Appearance: |
Transparent to translucent, in highly included stones
Yellowish green to greenish yellow to brownish green
An asteriated stone has been reported, but this is extremely rare |
| Misnomers: |
Evening emerald, night emerald, bastard emerald |
| Typical
Sizes: |
1 to over 5 ct; stones over 300 ct are known |
| Cut Styles: |
faceted, tumbled, beads |
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| IDENTIFICATION |
| Optic
Character: |
DR, biaxial positive or negative (the beta index is usually almost exactly halfway between the extremes) |
| Refractive
Index: |
1.654-1.690 (+/-.020) |
| Birefingence: |
.035 to .038, usually .036 |
| Dispersion: |
.020 |
| Pleochroism: |
Weak yellow-green and green; noticeable only in dark stones |
| Ultraviolet
Fluorescence: |
Inert |
| Absorption
Spectra: |
Three strong, narrow bands at 453, 477, and 497 nm |
| Cause
of Color: |
Iron |
| Specific
Gravity: |
3.34 (+.14, -.07) |
| Polish
Luster: |
Vitreous |
| Fracture: |
Conchoidal |
| Luster: |
Vitreous to subvitreous |
| Cleavage: |
Rarely seen; imperfect to distinct in one direction |
| Indentifying
Characteristics: |
Moderate doubling due to birefringence; disk-like liquid and gas inclusions ("lilypads"); dark octahedral chromite crystals |
| Known
Enhancements: |
None known |
| DURABILITY RATINGS |
| Hardness: |
6 1/2 to 7 |
| Toughness: |
Fair to good |
| Peridot is sometimes mistaken for: chrysoberyl, demantoid, diopside, precious beryl, moldavite, prasiolite, prehnite, sinhalite, emerald, tourmaline and vesuvianite |
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Care
Tips:
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| Cleaning Methods |
| •Ultrasonic: |
Risky |
| •Steamer: |
Never |
| •Warm
soapy water: |
Safe |
| Stability of Stone |
| •Heat
tolerance: |
Uneven or rapid heat may cause fracturing or complete breakage |
| •Light
tolerance: |
Stable |
| •Chemical tolerance: |
Attacked easily by sulfuric acid and less easily by hydrochloric acid; acid perspiration of some people may attack over a long period of time; pickling solution will etch the surface of the stone |
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Recommended
Uses:
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Rings
- Peridot is commonly used in rings despite its low tolerance to everyday abuse. Because peridot is proned to the occassional abrasion it is not highly recommended as a center stone for a ring. Granted, if a ring is preferred there are plenty of sizes and qualities to choose from. Economically, peridot is a great choice for a nice stone at an affordable price. Earrings
- Earrings are a great option for peridot. Due to the availability of peridot a set of matching stones should not be difficult to acquire. They can be easily matched and are perfect for a trio such as earrings and a pendant or ring. As with amethyst and garnet, checkerboard cuts are sometimes available and make for great earrings.
Pendants - Peridot is a good stone to be used in a pendant. Pendants are one of the more common uses of the stone due to the affordability of larger sizes. When considering a peridot pendant, pear shaped stones work well and are easily acquired.
Bracelet - It is recommended to use smaller sized stones when using peridot in a bracelet. Because bracelets are subjected to rough abuse larger stones in peridot do not wear well. If the bracelet is only worn occasionally then larger (4-5mm) stones will be fine. Although peridot is better suited for earrings or a pendant bracelets are not unheard of and are quite beautiful.
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Source
Map:
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| All technical specifications and care
tips on this page was referrenced from the "Gem
Reference Guide" published by the Gemological Institute
of America |
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