Peridot Clarity and Inclusions: What Buyers Should Know Before Purchasing

Understanding Peridot's Unique Mineralogy

Peridot, the gemstone variety of the mineral forsterite, belongs to the olivine group. Its chemical composition, (Mg, Fe)2SiO4, reflects a solid solution series between forsterite (magnesium-rich) and fayalite (iron-rich). The presence of iron is responsible for peridot's signature green color, ranging from yellow-green to olive to brownish-green. Unlike many gemstones that form in the Earth's crust, peridot crystallizes deep within the upper mantle, at depths of 20 to 55 kilometers, and reaches the surface through volcanic eruptions or tectonic activity. This mantle origin is a key factor in understanding its internal characteristics, as the extreme pressure and temperature conditions influence the types of inclusions and clarity features that gemologists observe.

Clarity Grading in Peridot: A Different Perspective

When evaluating peridot, clarity is often not the primary concern for buyers, but it still significantly affects value and durability. The Gemological Institute of America (GIA) clarity grading system, which ranges from Flawless to Included, is applied to peridot, but the grading criteria are modified because peridot is an 'eye-clean' gemstone in most commercial qualities. Eye-clean means that no inclusions are visible to the naked eye under normal viewing conditions, typically at a distance of about 15 centimeters. Most peridot sold in jewelry is eye-clean, but as with any gemstone, inclusions can be present and may impact the stone's transparency and brilliance.

The Role of Inclusions in Peridot

Inclusions in peridot are not merely flaws; they are geological fingerprints that reveal the gemstone's origin and formation history. For the informed buyer, understanding these inclusions can be a tool for authentication and sometimes even origin determination. Common inclusions in peridot include mineral crystals, fluid inclusions, and healing fissures. The most famous inclusion is the 'lily pad' inclusion, a disk-shaped fracture that surrounds a tiny crystal, often a chromite or a spinel. These lily pads are typical of peridot from San Carlos, Arizona, and they are frequently seen in stones from other localities as well.

How Inclusions Affect Value

Inclusion-heavy peridot is less valuable because inclusions can obscure transparency and reduce brilliance. However, the impact of inclusions is graded with more leniency than in stones like diamond or topaz. A few visible inclusions might only slightly reduce the price, whereas a heavily included peridot might be cut as a cabochon or even used in beads, where the inclusions are less of a detractor. For the buyer, the key is to look for a peridot that is eye-clean or has inclusions that are not visible without magnification. If an inclusion is visible, it should be located near the girdle or on the back of the stone, where it is less noticeable when set.

Common Inclusions Found in Peridot

Gemologists use magnification to observe internal features, and peridot presents a diverse array of them. Here is a detailed look at the most common inclusions:

• Mineral crystals: These are solid inclusions of other minerals that crystallized before or at the same time as the peridot. In peridot, common mineral inclusions include chromite, spinel, pyroxene, and olivine itself. They appear as dark, opaque, or transparent crystals, and their shape and color can help gemologists identify the mineral.
• Fluid inclusions: These are cavities filled with liquid or gas, often containing a bubble. They are formed when fluids are trapped during crystal growth. In peridot, fluid inclusions can be arranged in irregular patterns or form negative crystals that reflect the host's crystal shape.
• Fingerprints: These are networks of tiny fluid inclusions that resemble a human fingerprint. They are common in many gemstones, including peridot, and result from healing of internal fractures.
• Lily pad inclusions: This is the most characteristic inclusion in peridot. It is a disk-shaped stress fracture that surrounds a small crystal, typically chromite or spinel. Under magnification, the center crystal appears dark, surrounded by a thin, circular tension crack. These inclusions are named for their resemblance to lily pads floating on water.
• Twinning lines: Peridot can exhibit polysynthetic twinning, which appears as straight or angular lines that are often visible under magnification. These lines are not inclusions but are internal features that affect clarity.

Peridot Origins: How Inclusions Can Be Diagnostic

While peridot's mineral composition is consistent worldwide, the specific inclusions and their characteristics can sometimes indicate the gemstone's geographic origin. This is an advanced gemological technique that most buyers do not need to worry about, but it is interesting and useful for authentication. For instance, peridot from the San Carlos Apache Reservation in Arizona are known for their abundant lily pad inclusions, which are rarely seen in stones from other deposits. In contrast, peridot from Pakistan (Kashmir region) is known for its high clarity and often lacks prominent inclusions. Peridot from Myanmar (Burma) may contain distinctive mineral suites including ruby and spinel crystals. However, relying on inclusions for origin determination is not foolproof, because similar inclusions can occur in different localities, and some stones are cut from material that is free of diagnostic features. For the average buyer, the presence or absence of lily pads is not a reliable indicator of quality or value; it is simply a characteristic of certain deposits.

Practical Buying Guide: What to Look For

When shopping for peridot, follow these guidelines to ensure you get a beautiful stone that meets your expectations:

1. Prioritize Color Over Clarity

In peridot, color is the most important quality factor. The most desirable color is a rich, vivid green with a slight golden yellow hue, often described as 'olive' or 'lime' green. Stones with too much yellow can appear washed out, while those with too much brown may look muddy. Clarity is secondary: a eye-clean, medium-green stone is often more valuable than a flawlessly clean but pale stone. Inspect the stone in natural daylight to assess its true color, as artificial lighting can alter the appearance.

2. Assess Inclusions Under Magnification

Ask to see the stone under a 10x loupe. Look for inclusions that are visible to the naked eye, as these will affect the stone's appearance. Pay attention to their location: inclusions that are right under the table (the top facet) will be more visible and distracting. Inclusions near the girdle or the pavilion may be less noticeable when the stone is set. Large fractures or cracks can pose durability risks, especially during setting or cleaning. If you see a crack that extends to the surface, be cautious, as it could worsen with impact.

3. Know the Common Treatments

Peridot is typically not treated to enhance its color or clarity. It is one of the few gemstones that is almost always completely natural. However, some peridot may be oiled or resin-filled to mask fractures, but this is not a common practice for jewelry-grade stones. Also, note that some peridot on the market is actually a synthetic or imitation. Natural peridot is plentiful, so synthetic production is limited. Still, it is wise to purchase from a reputable jeweler and ask for a certificate if possible.

4. Consider Durability for Everyday Wear

Peridot has a hardness of 6.5 to 7 on the Mohs scale, which is relatively soft compared to other gems like sapphire (9) or diamond (10). It is also brittle and can be sensitive to sudden temperature changes. This means peridot is not recommended for daily wear rings; it is better suited for pendants, earrings, or occasional wear rings. When cleaning peridot, use warm soapy water and a soft brush. Avoid steam cleaners and ultrasonic cleaners, as they may shake the stone or cause it to fracture. Store peridot separately from harder gems to prevent scratches.

5. Scrutinize Cut and Proportions

A well-cut peridot should display good brilliance and symmetry. Inclusions can sometimes dictate the cut, but a good lapidary will orient the stone to minimize visible inclusions and maximize color. Look for a stone with a high polish and no nicks or chips. Avoid overly shallow or deep cuts, as they can lead to light leakage or dark windows, reducing the stone's fire.

Setting and Design Considerations

Given peridot's relative softness, the setting plays a crucial role in protecting the gemstone. Bezel settings offer the most protection because they surround the stone with metal, whereas prongs can leave the stone vulnerable to knocks. If you prefer a prong setting, ensure the prongs are sturdy and cover enough of the stone. For rings, consider a design that places the stone in a low-profile or recessed position. For earrings or pendants, peridot is safe as long as the piece is not subject to heavy impact.

Conclusion

Peridot is a beautiful and fascinating gemstone with a unique mantle origin. Clarity and inclusions play a role in its value, but the key to a successful purchase is understanding that color trumps clarity in this gem. Most peridot is eye-clean, and the inclusions present are often charming natural signatures, like lily pads, that do not detract from beauty. When buying peridot, prioritize a vivid green color, inspect the stone for visible or risky inclusions, and consider the durability limitations for the intended jewelry use. By being an informed buyer, you can select a peridot that offers both beauty and structural integrity, a gemstone that is not only stunning but also carries a piece of Earth's deep history.