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A purple-pink star sapphire displaying asterism in a platinum ring. An asterism (from Ancient Greek ἀστήρ (astḗr) 'star' and -ism) is a star-shaped concentration of light reflected or refracted from a gemstone. It can appear when a suitable stone is cut en cabochon (i.e. shaped and polished, not faceted). A gemstone that exhibits this ...
In gemology, chatoyancy (/ ʃəˈtɔɪ.ənsi / shə-TOY-ən-see), also called chatoyance or the cat's eye effect, [1] is an optical reflectance effect seen in certain gemstones, woods, and carbon fiber. Coined from the French œil de chat, meaning 'cat's eye'. The chatoyant effect is typically characterized by one or more well-defined bands of ...
The general definition of opalescence is a milky iridescence displayed by an opal, which describes the visual effect of precious opal very well, and opalescence is commonly used in lay terms as a synonym for iridescence.
Lustre (mineralogy) Lustre (British English) or luster (American English; see spelling differences) is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back to the Latin lux, meaning "light", and generally implies radiance, gloss, or brilliance. A range of terms are used to describe lustre ...
Crystal twinning. Quartz – Japan twin. Diagram of twinned crystals of albite. On the more perfect cleavage, which is parallel to the basal plane (P), is a system of fine striations, parallel to the second cleavage (M). Crystal twinning occurs when two or more adjacent crystals of the same mineral are oriented so that they share some of the ...
Peridotite. Peridotite (US: / ˈpɛrɪdoʊˌtaɪt, pəˈrɪdə -/ PERR-ih-doh-tyte, pə-RID-ə-) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg 2+), reflecting the high proportions of ...
Some of the most typical are small inclusions, or cuts, in the container the crystal is being grown on. This includes scratches on the sides and bottom of glassware. A common practice in crystal growing is to add a foreign substance, such as a string or a rock, to the solution, thereby providing nucleation sites for facilitating crystal growth ...
Like Chardin's griffin or eagle, some stories about luminous gems involve animals other than snakes and dragons. An early example is the 3rd-century CE Greek Pseudo-Callisthenes Romance of Alexander that says Alexander the Great once speared a fish, "in whose bowels was found a white stone so brilliant that everyone believed it was a lamp.