Podcast
Questions and Answers
What is the primary factor that determines a gem's density and specific gravity?
What is the primary factor that determines a gem's density and specific gravity?
What can the exterior shape of a crystal indicate?
What can the exterior shape of a crystal indicate?
Why are some gems rare?
Why are some gems rare?
What is twinning the result of?
What is twinning the result of?
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What can inclusions in a colored stone help identify?
What can inclusions in a colored stone help identify?
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What determines a gem's reaction to external stress?
What determines a gem's reaction to external stress?
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Study Notes
Crystal Systems and Identification
- Crystalline minerals are classified into 7 crystal systems based on the symmetry of their unit cells.
- Recognizable crystal shapes of rough gemstones can help identify them.
- The exterior shape of a crystal often indicates its symmetry at an atomic level.
Factors Affecting Gemstone Shapes and Sizes
- Shapes and sizes of rough gem crystals affect the shapes and sizes of finished stones.
- Rarity of gems is due to the requirement of rare chemical elements or unique geological conditions, or both, to form.
Physical Properties of Gems
- A gem's density and specific gravity depend on the types of atoms it's made of, and how closely they're packed together.
- Twinning can occur due to a change during crystal growth, or from cooling or pressure after the crystal has grown.
Fracture and Inclusions
- Different ways a gem breaks are called cleavage, parting, and fracture.
- Inclusions in a colored stone can help identify it as natural or man-made, untreated or treated.
- A gem's crystal structure determines its reaction to external stress.
- Large inclusions can dramatically affect beauty, value, and durability.
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Description
Learn about the classification of crystalline minerals into seven crystal systems and how the exterior shape of a crystal indicates its symmetry. Discover how the shapes and sizes of rough gem crystals affect the finished stones.
