star sapphire
Definition
Noun: A star sapphire is a type of sapphire gemstone that, when cut and polished into a smooth, rounded shape (typically a cabochon), displays a luminous, star-like pattern on its surface. This optical phenomenon, called asterism, is caused by light reflecting from needle-like inclusions of the mineral rutile within the gem's crystalline structure.
Usage
The term is used to specifically describe sapphires exhibiting the star effect. It functions as a countable noun. * Gemologists classify a star sapphire based on the sharpness and symmetry of its asterism. * The most prized star sapphires have a sharp, six-rayed star centered on the top of the gem. * She inherited a beautiful ring featuring a blue star sapphire.
Advanced Usage
- Quality Descriptors: The term is often modified by adjectives describing the star's quality (e.g., , ) or the gem's body color (e.g., , ).
- Scientific Context: In mineralogy, the term specifies a variety of corundum (the mineral species for sapphire) characterized by asterism.
Variants and Related Words
- Star ruby: The red variety of corundum (ruby) that exhibits the same asterism effect.
- Asterism: The technical name for the star-shaped light reflection seen in some gemstones.
- Cabochon: The dome-shaped, polished cut without facets, which is required to display the star effect in a star sapphire.
Synonyms
- Asteriated sapphire (a more technical synonym).
Antonyms
- Faceted sapphire (a sapphire cut with flat, polished faces to maximize brilliance, which would not show a star).
Related Phrases/Idioms
- Star stone: A general, informal term for any gemstone displaying asterism, which can include star sapphires, star rubies, and others.
Noun
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a sapphire that when cut shows a starlike figure in reflected light because of its crystalline structure
