Unlock the Secrets: A Comprehensive Guide to Identifying Gemstones

Identifying gemstones can be a fascinating and rewarding pursuit, whether you’re a budding collector, a curious hobbyist, or simply want to know more about the sparkling stones in your jewelry. While professional gemologists use sophisticated equipment, there are several tests and observations you can perform at home to narrow down the possibilities. This comprehensive guide will walk you through the process step-by-step, providing you with the knowledge and tools to confidently identify a variety of gemstones.

Understanding Gemstone Properties

Before diving into identification techniques, it’s crucial to understand the key properties that differentiate one gemstone from another. These properties are the building blocks of gemstone identification:

* **Color:** While seemingly straightforward, color can be complex. Gemstones can exhibit different colors depending on the viewing angle (pleochroism) or the type of light source. Also, color can be affected by impurities in the stone.
* **Transparency:** This refers to how well light passes through the gemstone. Gemstones can be transparent (clear, allowing light to pass through easily), translucent (allowing some light to pass through, but not clearly), or opaque (not allowing light to pass through at all).
* **Luster:** Luster describes how light reflects off the surface of a gemstone. Common types of luster include: Adamantine (diamond-like), Vitreous (glass-like), Metallic, Silky, Resinous, Pearly, and Waxy.
* **Refractive Index (RI):** A measure of how much light bends as it passes from air into the gemstone. This is a key property that requires specialized equipment (refractometer) for precise measurement, but you can estimate it based on the gemstone’s brilliance and ‘sparkle’. High RI generally means more brilliance.
* **Birefringence:** The difference between the maximum and minimum refractive indices of a doubly refractive gemstone. This property can be observed using a polariscope.
* **Dispersion (Fire):** The ability of a gemstone to split white light into its spectral colors (like a prism). Diamond is known for its high dispersion, resulting in flashes of rainbow colors.
* **Hardness:** A gemstone’s resistance to scratching. Measured on the Mohs Hardness Scale (1-10), with 1 being the softest (talc) and 10 being the hardest (diamond).
* **Specific Gravity (SG):** The ratio of the weight of a gemstone to the weight of an equal volume of water. This can be determined using hydrostatic weighing.
* **Cleavage:** The tendency of a gemstone to break along specific crystallographic planes, resulting in smooth, flat surfaces.
* **Fracture:** The way a gemstone breaks when it doesn’t cleave. Common types of fracture include: Conchoidal (shell-like), Uneven, Hackly (jagged), and Splintery.
* **Crystal System:** Gemstones form in different crystal systems (e.g., cubic, tetragonal, hexagonal, orthorhombic, monoclinic, triclinic). The crystal system influences the gemstone’s properties and appearance.

Essential Tools for Gemstone Identification

While advanced equipment is used by professionals, you can get started with a few basic tools:

* **Magnifying Loupe (10x):** Essential for examining inclusions, surface features, and imperfections. A 10x magnification is standard for gemological observation.
* **Bright Light Source:** Natural daylight is ideal, but a strong, focused lamp (preferably with adjustable intensity) is also necessary.
* **Hardness Testing Kit:** Includes a set of hardness picks or pencils with known Mohs hardness values. Use with extreme caution to avoid damaging the gemstone. It is advisable to avoid this test on valuable or mounted stones.
* **Streak Plate:** An unglazed porcelain tile used to determine the streak color of a gemstone. The streak color is the color of the gemstone’s powder when scratched against the plate.
* **Specific Gravity Liquids (optional):** A set of heavy liquids with known specific gravities can be used to estimate a gemstone’s SG.
* **Polariscope (optional):** A device used to determine if a gemstone is singly or doubly refractive. It can also help identify anomalous double refraction due to strain in a singly refractive gemstone.
* **Dichroscope (optional):** Used to observe pleochroism (different colors depending on the viewing angle) in gemstones.
* **Refractometer (optional):** A precise instrument for measuring the refractive index of a gemstone. It requires specialized knowledge and training to use effectively.
* **Spectroscope (optional):** An instrument that analyzes the spectrum of light absorbed by a gemstone, revealing its chemical composition.
* **Calipers:** For accurately measuring the dimensions of a gemstone.
* **Microscope (optional):** Higher magnification allows for detailed examination of inclusions and other internal features.

Step-by-Step Gemstone Identification Process

Follow these steps to systematically identify your gemstone:

**Step 1: Initial Observation and Recording**

* **Color:** Note the primary color of the gemstone. Is it consistent throughout, or are there variations? Are there secondary colors present?
* **Transparency:** Is the gemstone transparent, translucent, or opaque?
* **Luster:** Observe how light reflects off the surface. Is it glassy, metallic, or something else?
* **Shape and Cut:** Describe the shape and cut of the gemstone (e.g., round brilliant, emerald cut, cabochon). The cut can sometimes offer clues to the gemstone’s identity.
* **Size and Weight:** Measure the dimensions of the gemstone (length, width, depth) and weigh it in carats (if possible). These measurements can be helpful in calculating specific gravity.
* **Setting:** Is the gemstone set in jewelry? If so, the setting may provide clues about the gemstone’s value or period of origin. Be careful removing a gemstone from a setting, it’s best left to professionals.

**Step 2: Magnification and Inclusion Analysis**

* **Use a 10x Loupe:** Carefully examine the gemstone under magnification. Look for inclusions (internal imperfections), surface blemishes, and other distinguishing features.
* **Types of Inclusions:** Note the type, shape, and distribution of any inclusions. Some common types of inclusions include:
* **Crystals:** Tiny crystals of other minerals trapped within the gemstone.
* **Needles:** Long, thin, needle-like inclusions.
* **Bubbles:** Gas bubbles trapped within the gemstone (common in synthetic stones).
* **Feathers:** Fractures that resemble feathers.
* **Zoning:** Variations in color or clarity within the gemstone, often reflecting its growth history.
* **Inclusion Patterns:** The arrangement and type of inclusions can be diagnostic for certain gemstones. For example, horsetail inclusions are characteristic of demantoid garnet.

**Step 3: Hardness Testing**

* **Locate an Inconspicuous Area:** Choose a small, inconspicuous area on the gemstone to perform the hardness test. The pavilion (bottom) of the stone is often a good choice.
* **Use Hardness Picks or Pencils:** Start with a hardness pick or pencil that you believe is softer than the gemstone. Gently try to scratch the gemstone’s surface.
* **Observe the Results:** If the pick scratches the gemstone, it is softer than the pick. If the pick does not scratch the gemstone, it is harder than the pick.
* **Progress Incrementally:** Continue testing with progressively harder picks until you find one that scratches the gemstone. This will give you an approximate Mohs hardness value.
* **Caution:** Exercise extreme caution when performing hardness tests. Use minimal pressure and avoid testing on valuable or mounted stones. Diamond is known for being hardest and therefore, should not be used in this test.

**Mohs Hardness Scale (Simplified):**

* 1: Talc
* 2: Gypsum
* 3: Calcite
* 4: Fluorite
* 5: Apatite
* 6: Orthoclase Feldspar
* 7: Quartz
* 8: Topaz
* 9: Corundum (Sapphire and Ruby)
* 10: Diamond

**Step 4: Streak Testing**

* **Use a Streak Plate:** Rub the gemstone across the surface of an unglazed porcelain streak plate.
* **Observe the Streak Color:** Note the color of the powder left behind on the streak plate. The streak color can be different from the gemstone’s body color. For instance, Hematite is black but produces a reddish brown streak.
* **Considerations:** This test is most effective for gemstones with a hardness lower than that of the streak plate (approximately 7 on the Mohs scale). Gemstones harder than the streak plate will simply scratch the plate.

**Step 5: Specific Gravity Determination (Hydrostatic Weighing)**

* **Weigh the Gemstone in Air:** Use a sensitive scale to weigh the gemstone in air. Record the weight in grams.
* **Weigh the Gemstone in Water:** Suspend the gemstone from a fine thread or wire and immerse it completely in water. Weigh it again while submerged. Record the weight in grams.
* **Calculate Specific Gravity:** Use the following formula:
* SG = Weight in Air / (Weight in Air – Weight in Water)
* **Compare to Known Values:** Compare the calculated specific gravity to known values for different gemstones. Specific gravity is a reliable diagnostic property.

**Step 6: Advanced Testing (Optional – Requires Specialized Equipment)**

* **Refractive Index (RI) Measurement:** Use a refractometer to measure the refractive index of the gemstone. This is a highly accurate method of identification, but it requires careful technique and a suitable refractometer liquid.
* **Polariscope Examination:** Observe the gemstone under a polariscope to determine if it is singly or doubly refractive. Doubly refractive gemstones will show interference colors or patterns when rotated between crossed polarizers. Singly refractive gemstones will remain dark.
* **Dichroscope Examination:** Use a dichroscope to look for pleochroism (different colors depending on the viewing angle). This is most useful for colored gemstones.
* **Spectroscopic Analysis:** Use a spectroscope to analyze the absorption spectrum of the gemstone. This can reveal the presence of specific chemical elements that cause its color.

Common Gemstones and Their Identifying Characteristics

Here’s a brief overview of some common gemstones and their key identifying characteristics:

* **Diamond (C):** Hardness 10, Adamantine luster, High dispersion (fire), Singly refractive, Typically colorless or with slight yellow or brown tint. High refractive index. Can be identified by its extreme hardness, brilliance and dispersion.
* **Ruby (Al2O3):** Hardness 9, Vitreous luster, Red color (due to chromium), Doubly refractive, Pleochroism (red/orange-red). Belongs to Corundum family. Inclusions include needles and crystals.
* **Sapphire (Al2O3):** Hardness 9, Vitreous luster, Blue color (due to iron and titanium), Doubly refractive, Pleochroism (blue/green-blue). Belongs to Corundum family. Can come in a variety of colors (pink, yellow, green, etc).
* **Emerald (Be3Al2Si6O18):** Hardness 7.5-8, Vitreous luster, Green color (due to chromium or vanadium), Doubly refractive, Inclusions often present (jardin).
* **Aquamarine (Be3Al2Si6O18):** Hardness 7.5-8, Vitreous luster, Blue to blue-green color (due to iron), Doubly refractive, Part of the Beryl family, like Emerald.
* **Garnet (X3Y2(SiO4)3):** Hardness 6.5-7.5, Vitreous luster, Wide range of colors (red, green, orange, yellow, brown), Singly refractive (except for andradite). A group of minerals rather than a single one.
* **Amethyst (SiO2):** Hardness 7, Vitreous luster, Purple color (due to iron and irradiation), Doubly refractive, Part of the Quartz family.
* **Citrine (SiO2):** Hardness 7, Vitreous luster, Yellow to orange color (due to iron), Doubly refractive, Part of the Quartz family.
* **Topaz (Al2SiO4(OH,F)2):** Hardness 8, Vitreous luster, Wide range of colors (colorless, blue, yellow, brown, pink), Doubly refractive.
* **Peridot ((Mg,Fe)2SiO4):** Hardness 6.5-7, Vitreous luster, Olive green color (due to iron), Doubly refractive.
* **Tourmaline (Complex Borosilicate):** Hardness 7-7.5, Vitreous luster, Wide range of colors, Doubly refractive, Strong pleochroism.
* **Opal (SiO2·nH2O):** Hardness 5.5-6.5, Vitreous to resinous luster, Play of color (iridescence), Amorphous (no crystal structure).
* **Pearl (CaCO3):** Hardness 2.5-4.5, Pearly luster, White, cream, or colored, Organic gemstone.
* **Jade (Jadeite or Nephrite):** Hardness 6.5-7 (Jadeite), 6-6.5 (Nephrite), Greasy to vitreous luster, Green, white, or other colors, Tough (resistant to breakage).
* **Turquoise (CuAl6(PO4)4(OH)8·4H2O):** Hardness 5-6, Waxy to dull luster, Blue to green color (due to copper), Opaque.

Distinguishing Natural, Synthetic, and Imitation Gemstones

It’s important to be able to distinguish between natural, synthetic (lab-created), and imitation gemstones:

* **Natural Gemstones:** Formed in the Earth’s crust through natural geological processes. They often contain inclusions and imperfections.
* **Synthetic Gemstones:** Created in a laboratory with the same chemical composition and crystal structure as their natural counterparts. They may have fewer inclusions and more uniform color, although skilled manufacturers can now create synthetic stones with realistic-looking inclusions.
* **Imitation Gemstones:** Made of materials that resemble gemstones but have a different chemical composition and crystal structure. Examples include glass, plastic, and cubic zirconia. They generally have lower hardness, luster, and specific gravity than natural gemstones.

**Clues for Identifying Synthetic Gemstones:**

* **Unnatural Color:** Some synthetic gemstones have colors that are rarely or never found in nature.
* **Curved Striae:** Curved growth lines or striae may be visible under magnification in some synthetic gemstones.
* **Gas Bubbles:** Spherical gas bubbles are often present in imitation glass stones and some synthetic gemstones.
* **Unusually High Clarity:** Synthetic gemstones may be exceptionally clear and free of inclusions.

**Clues for Identifying Imitation Gemstones:**

* **Low Hardness:** Imitation gemstones are often softer than natural gemstones.
* **Low Refractive Index:** Imitation gemstones may have a lower refractive index, resulting in less brilliance and sparkle.
* **Plastic or Glassy Appearance:** Imitation gemstones may look artificial or lack the depth and luster of natural gemstones.

Tips for Buying Gemstones

* **Buy from Reputable Dealers:** Purchase gemstones from trusted jewelers or gem dealers with a good reputation.
* **Ask for a Gemological Certificate:** A certificate from a recognized gemological laboratory (e.g., GIA, AGS, EGL) provides an independent assessment of the gemstone’s quality and authenticity.
* **Examine the Gemstone Carefully:** Use a loupe to inspect the gemstone for inclusions, blemishes, and other imperfections. Check for any signs of treatment or enhancement.
* **Compare Prices:** Research the market value of similar gemstones to ensure you are getting a fair price.
* **Trust Your Instincts:** If something seems too good to be true, it probably is. Be wary of unusually low prices or pushy sales tactics.

Conclusion

Identifying gemstones is a skill that requires practice, patience, and attention to detail. By understanding the key properties of gemstones, using the right tools, and following a systematic approach, you can significantly improve your ability to identify a wide variety of stones. Remember to always exercise caution when performing hardness tests and consult with a professional gemologist if you have any doubts or concerns. With time and experience, you’ll unlock the secrets of the gem world and gain a deeper appreciation for these natural treasures.