Gemstones

Definition and characteristics: Definition: Gemstones are minerals or other materials that are: - Beautiful (color, luster, transparency, etc.) - Durable (hard enough to wear, resistant to damage) - Rare (or at least not too common) - Suitable for cutting and polishing Precious vs. Semi-Precious: Traditional classification: - Precious: Diamond, ruby, sapphire, emerald (the "big four") - Semi-Precious: All others (though this term is less used now, as many "semi-precious" gems are very valuable) Gem vs. Mineral: Not all minerals are gems, and not all gems are minerals: - Most gems are minerals (diamond, ruby, etc.) - Some gems are organic (pearl, amber, coral) - Some minerals are never gems (too common, not beautiful, etc.) Gem Varieties: Some minerals have multiple gem varieties: - Corundum: Ruby (red), sapphire (other colors) - Beryl: Emerald (green), aquamarine (blue), morganite (pink), etc. - Quartz: Amethyst, citrine, ametrine, many others Value Factors: Color, clarity, cut, carat weight (the "4 Cs" for diamonds, similar principles for colored gems), rarity, and origin all affect value.

The "big four" precious gems: Diamond: - Hardest mineral (10 on Mohs scale) - Composed of pure carbon - Valued for brilliance, fire, and durability - Colorless is most common, but fancy colors (blue, pink, etc.) are very rare and valuable - Graded by 4 Cs: Cut, Color, Clarity, Carat - Major sources: Africa, Russia, Canada, Australia Ruby: - Red variety of corundum (Al₂O₃) - Very hard (9), excellent durability - Valued for intense red color - Most valuable when pure red with slight purple (pigeon's blood) - Major sources: Myanmar, Thailand, Mozambique, Madagascar Sapphire: - All colors of corundum except red (which is ruby) - Blue is most valued, but other colors (pink, yellow, padparadscha) are also valuable - Very hard (9), excellent durability - Can show asterism (star effect) or color change - Major sources: Sri Lanka, Madagascar, Australia, Montana (USA) Emerald: - Green variety of beryl (Be₃Al₂Si₆O₁₈) - Valued for intense green color - Almost always has inclusions (jardin) - Softer than corundum (7.5-8), requires more care - Major sources: Colombia, Zambia, Brazil, Afghanistan Value: These four gems command the highest prices, especially in high quality and large sizes.

Other important gem materials: Topaz: - Hard (8), comes in many colors - Blue topaz is popular and affordable (usually treated) - Natural blue is very rare - Imperial topaz (pink-orange) is highly valued Tourmaline: - Very wide color range (almost every color) - Can be bi-colored or tri-colored - Strong pleochroism - Some varieties are very valuable (Paraiba tourmaline - neon blue/green) Garnet: - Group of related minerals - Many colors: red (pyrope, almandine), green (tsavorite, demantoid), orange (spessartine) - Some varieties very valuable (demantoid, tsavorite) Amethyst: - Purple variety of quartz - Popular and affordable - Can be very dark (Siberian) or light - Some show color zoning Citrine: - Yellow to orange variety of quartz - Natural citrine is rare (most is heat-treated amethyst) - Popular and affordable Opal: - Valued for play-of-color (rainbow flashes) - Can be very valuable (black opal from Australia) - Requires care (softer, can crack if dried) Pearl: - Organic gem, formed by mollusks - Natural pearls are very rare and valuable - Cultured pearls are more common - Valued for luster and color Many Others: Tanzanite, alexandrite, spinel, peridot, and many more are popular and collectible.

Key properties for gem identification: Hardness: Resistance to scratching (Mohs scale). Important for durability: - Very hard (9-10): Diamond, corundum - excellent for daily wear - Hard (7-8): Topaz, beryl, spinel - good for jewelry - Medium (5-7): Opal, turquoise - require more care Refractive Index: How much light bends when entering the gem. Measured with a refractometer. Very useful for identification. Specific Gravity: Density relative to water. Can help distinguish similar-looking gems. Color: Hue (the color itself), tone (lightness/darkness), and saturation (intensity). Very important for value. Clarity: Presence of inclusions and flaws. Some gems (like emerald) are expected to have inclusions. Phenomena: Special optical effects: - Asterism: Star effect (star ruby, star sapphire) - Chatoyancy: Cat's eye effect - Play-of-Color: Rainbow flashes (opal) - Color Change: Different colors in different light (alexandrite) Identification: Professional gemologists use multiple properties and often advanced equipment. For collectors, basic properties and visual examination are usually sufficient.

How gems are improved: Heat Treatment: Most common treatment. Heating improves color or clarity. Usually permanent. Very common for sapphire, ruby, tanzanite, topaz. Often undetectable. Irradiation: Exposing to radiation changes color. Used for blue topaz, some diamonds. Some treatments are stable, others fade. Fracture Filling: Filling cracks with glass, resin, or oil. Common in emerald, ruby, some diamonds. Improves appearance but requires special care. Dyeing: Adding color to porous materials. Common in jade, turquoise, some pearls. Usually detectable and may fade. Coating: Thin films on surface to change color. Can wear off. Must be disclosed. Disclosure: All treatments must be disclosed to buyers. Federal Trade Commission requires this. Reputable dealers provide full disclosure. Value Impact: Treatments generally reduce value compared to untreated gems. However, some treatments (like heat treatment of sapphire) are expected and widely accepted. For Collectors: Understanding treatments helps make informed purchases and care for gems properly. Some treatments require special care.

Caring for your gemstones: Cleaning: - Most gems: Warm soapy water, soft brush, rinse well - Ultrasonic cleaners: Safe for most gems, but avoid for: - Fracture-filled gems (can remove filler) - Opal (can crack) - Pearls (can damage) - Steam cleaners: Safe for most, but avoid for same as ultrasonic Storage: - Store separately to prevent scratching - Soft pouches or individual compartments - Avoid extreme temperature changes - Some gems fade in light (store in dark) Wearing: - Remove before activities that could cause damage - Avoid harsh chemicals - Some gems are more delicate (opals, pearls, emeralds) - Harder gems (diamond, corundum) are more durable Professional Care: - Periodic professional cleaning - Check settings regularly (prongs can wear) - Re-polish if needed (for softer gems) - Re-oil emeralds if needed (if oiled) Insurance: Valuable gems should be insured. Get professional appraisals and keep documentation. For Collectors: Proper care preserves value and beauty. Understanding your gems' properties helps you care for them appropriately. Some gems require more care than others.