THE JOURNAL / Gemstone Identifier
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THE READING ROOM / 08Types of Opal: A Guide to Varieties and Color Patterns
Learn how common opal varieties differ, what visible patterns can suggest, and which questions require expert testing.
Read the guideTypes of Quartz: A Guide to Varieties, Colors, and Clues
Explore major quartz varieties, how their colors and patterns form, and what visible features can—and cannot—reveal about a specimen.
Read the guideTypes of Sapphire: Colors, Varieties, and Key Differences
Explore sapphire colors, varieties, and optical effects, plus the visible clues that help distinguish them from what requires gemological testing.
Read the guideTypes of Tourmaline: A Guide to Colors, Varieties, and Visual Clues
Explore major tourmaline varieties, from vivid Paraíba and watermelon stones to color-changing gems, and learn what appearance can—and cannot—reveal.
Read the guideWhat Are Gemstone Inclusions?
Learn what gemstone inclusions are, how they form, what they can reveal, and why visible features alone cannot confirm a gem’s identity or value.
Read the guideWhat Can a Gemologist Tell from a Photograph?
Learn which gemstone clues a photograph can reveal, where visual identification becomes uncertain, and when in-person gemological testing is needed.
Read the guideWhat Causes Labradorite Flash? The Science of Labradorescence
Labradorite flash comes from light interacting with microscopic internal layers, producing color that shifts as the stone or viewing angle changes.
Read the guideWhat Causes Opal Play of Color?
Learn how opal’s internal silica structure creates shifting flashes of color, and what visible patterns can—and cannot—tell you about a stone.
Read the guideWhat Is a Crystal Habit? Understanding Mineral Shapes and Growth Patterns
Learn what crystal habit means, how common mineral shapes form, and what a specimen’s visible growth pattern can—and cannot—tell you.
Read the guideWhat Is Adularescence? The Moonlike Glow in Moonstone
Learn what adularescence is, why moonstone seems to glow, how it differs from similar gem effects, and what identification can—and cannot—show.
Read the guideWhat Is Asterism in Gemstones? How Star Gems Get Their Glow
Learn what causes asterism, which gemstones can show a star, and how to distinguish visible clues from professional gem identification.
Read the guideWhat Is Chatoyancy in Gemstones?
Learn how chatoyancy creates a moving, eye-like band of light, which gems can show it, and how to distinguish visible clues from gemological confirmation.
Read the guideWhat Is Crackle Quartz? Appearance, Treatment, and Lookalikes
Learn how crackle quartz gets its fractured appearance, what you can observe, and what requires professional gem testing.
Read the guideWhat Is Gemstone Luster? A Guide to How Gems Reflect Light
Learn what gemstone luster means, how it differs from brilliance and shine, and what surface appearance can—and cannot—tell you about a gem.
Read the guideWhat Is Goldstone Made Of?
Goldstone is a man-made, glittering glass whose metallic sparkle comes from tiny copper crystals formed during cooling.
Read the guideWhat Is Opalite Made Of? Composition, Appearance, and Lookalikes
Learn what opalite is made of, how it differs from natural opal, and which visible clues can—and cannot—identify it.
Read the guideWhat Is Pleochroism in Gemstones?
Learn how pleochroism makes a gemstone show different colors from different directions, how to observe it, and what the effect can—and cannot—tell you.
Read the guideWhat Is Sea Glass? How It Forms and How to Identify It
Learn how sea glass forms, what its frosted surface can reveal, and how to distinguish it from similar materials without relying on appearance alone.
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