asterism, in mineralogy, starlike figure exhibited in light reflected or transmitted by some crystals.
What gems can have asterism?
Common examples of gems with asterism are ruby and sapphire with six-pointed stars caused by tiny exsolution rutile needles, or black diopside with four-pointed stars produced by exsolution inclusions of black magnetite. Rose quartz, garnets, moonstone and other gems can also have asterism effect.
What is a Starstone?
Definition of starstone : an asteriated stone especially : star sapphire.
What is an example of an asterism?
The Summer Triangle is an example of an asterism: a group of stars that form a recognizable pattern or shape. The Big Dipper, the Little Dipper and the Great Square of Pegasus are other examples of asterisms.
What causes asterism in stones?
The star-effect or “asterism” is caused by the difference in refractive index between the host material and that of the dense inclusions of tiny fibers of rutile (also known as “silk”). The stars are caused by the light reflecting from needle-like inclusions of rutile aligned perpendicularly to the rays of the star.
What is the difference between Constellation and asterism?
Constellations are patterns of stars visible to the unaided eye, or regions of space seen from Earth that are bounded by borders designated by the International Astronomical Union. Asterisms are also naked-eye star patterns, but they do not form constellations on their own.
What is asterism in gemstone?
An asterism (from Ancient Greek ἀστήρ (aster) ‘star’) is a star-shaped concentration of reflected or refracted light from a gemstone. Asterisms can appear when a suitable stone is cut en cabochon i.e. shaped and polished (not faceted). A gemstone that exhibits this effect is referred to as a star stone or asteria.
Where are moonstones found?
The finest moonstones are found mainly in Sri Lanka and Southern India. Other varieties occur Australia, Armenia, Mexico, Brazil, and the United States. The rainbow variety of moonstone can be found in India and Madagascar.
How are moonstones formed?
Moonstone is a variety of the feldspar-group mineral orthoclase. Then, as the newly formed mineral cools, the intergrown orthoclase and albite separate into stacked, alternating layers. When light falls between these thin, flat layers, it scatters in many directions, producing the phenomenon called adularescence.
What causes asterism in crystals?
Asterism is generated by reflections of light from twin-lamellae or from extremely fine needle-shaped acicular inclusions within the stone’s crystal structure. A common cause is oriented sub-microscopic crystals of rutile within the gem mineral. The star-effect may be also caused by the inclusions of hematite.
Is Starstone real?
A star stone is a gemstone which has been cut and polished in a way which takes advantages of natural inclusions in the stone which create a very distinctive star pattern when light reflects from the stone. Many star stones are sapphires, although rubies and many quartzes can be turned into star stones as well.
What is asterism in gemology?
Asterism (gemology) Asterism (from Ancient Greek: ἀστήρ star ), the property of a star stone ( asteria ), is the phenomenon of gemstones exhibiting a star-like concentration of reflected or refracted light when cut en cabochon (shaped and polished rather than faceted ).
What is asterism on a Star Sapphire?
Asterism on the surface of a blue star sapphire. Asterism (from Ancient Greek: ἀστήρ star), the property of a star stone (asteria), is the phenomenon of gemstones exhibiting a star-like concentration of reflected or refracted light when cut en cabochon (shaped and polished rather than faceted).
What is the scientific name for a star shaped gemstone?
For the Star Ruby grapefruit variety, see Grapefruit § Star Ruby. An asterism (from Ancient Greek: ἀστήρ, aster, meaning ‘star’) is a star-shaped concentration of reflected or refracted light from a gemstone. Asterisms can appear when a suitable stone is cut en cabochon i.e. shaped and polished (not faceted ).
What does the asterism mean in typography?
Asterism (typography) In typography, an asterism (” group of stars “) is the typographic symbol consisting of three asterisks placed in a triangle: ⁂ . Now rarely used or near-obsolete its purpose is to “indicate minor breaks in text,” call attention to a passage, or to separate sub-chapters in a book.
