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| a flat face cut and polished on a gemstone |
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to shape or cut (and usually polish) the material for adornment or ornamental use
includes faceting and carving |
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| a non-facted gemstone cut which consists of a domes and polished top surface with a flat, unpolished back |
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| an effect in the brain produced by reaction to visible light that reaches the back of the eye; the reaction triggers messages to the brain and color is 'seen' |
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| material through which an object can be viewed clearly and distinctly |
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| material through which an object can be viewed indistinctly or not at all, but through which light can be transmitted |
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| material that allows no light to be trasnmitted |
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| a surface reflection, the brightness and quality of which to some extent depends upon the refractive index and the polish or surface condition of the material |
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| the very high reflective luster shown by metals such as gold and silver, and by gem materials such as polished hematite and pyrite |
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| a very bright and reflective luster, typically displayed by diamond |
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| bright luster, often from gemstones having high refractive indices such as zircon and demantoid garnet |
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a glossy luster, equal to or even brighter than highly polished glass
Ex) polished ruby and sapphire |
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the luster seen in polished glass, and in most transparent gemstones whose refractive indices fall within the middle range of values
Ex) emerald, tourmaline |
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| the luster of certain fibrous minerals such as gypsum and malachite |
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the luster shown by certain gem materials that are soft and that have low refractive indices
Ex) amber |
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| the wax-like luster which may be shown, for example, by certain microcrystalline gem materials such as turquoise, and by soft gem materials of organic origin such as jet |
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observable and measurable characteristics of materials relating to internal and external physical energy and forces
Ex) optical properties, density, hardness |
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those physical properties relating to behaviour under visible light
Ex) transparency, reflection, refraction, color, luster |
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'cat's-eye effect'
an internal reflection effect which appears as a bright band of light across the surface of certain gemstones when cut as cabochons
the reflection is from fine inclusions, all parallel to one direction, and is visible when the base of the cabochon is cut in parallel with the direction of the inclusions |
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Definition
a star-like reflection of intersecting band of light which is seen from the surface of certain gems when they cut in a particular crystallographic orientation as cabochons
an internal reflection effect caused by reflections from two or more sets of parallel fibrous or channel inclusions |
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play-of-color
iridescence is a color, or serious of colors produced by interference or diffraction when visible light is reflected or diffracted from thin layers or from the internal structures of gems such as labradorite or precious opal |
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a popular term for the spectral colors displayed by a gemstone with a significant degree of dispersion
Ex) diamond |
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| Internal Reflection Effects |
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| optical effects caused by the reflection of light from features below the surface of a gemstone |
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internal visible features within cut or uncut gem materials
inclusions may be crystals, cavities, bubbles, fragments, fractures, healed fractures, incipient cleavage, swirls and striations |
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| Single, Monophase Inclusion |
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| an inclusion of a single liquid or gas or solid |
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| inclusions made up of a combination of a liquid and gas, or a gas and solid, or a solid and liquid |
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| inclusions made up on liquid, gas and solid |
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a magnifying lens, ideally of 10x power for the observation of most gem materials
the most important instrument used by gemmologists outside a laboratory |
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| actinolite crystal, resembling the shape of bamboo, for example, in emerald |
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| intersecting cleavage fissures in moonstone |
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| a partially-healed fracture or fissure or a group of small particles trapped during the natural growth process or synthesis |
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| fibrous inclusions, radiating form a nucleus in demantoid garnet |
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| partially healed tension cracks around a crystal or cavity in peridot |
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| thin ro-like crystal inclusion |
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| thin straight tubes orientated parallel to each other in beryl |
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| fine rutile inclusions that may cause a hazy appearance in the stone, seen especially in corundum |
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| witish crystallites on a dark background, especially in obsidian |
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| tension cracks resulting in a radial pattern, for example in amber |
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| ribbon-like rows of partial healing along twinning planes in quartz |
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| fine fluid inclusions, often join together in a web; may be two-plase; seen in tourmalines |
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| Bright-field Illumination |
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Definition
the object is illuminated from directly below, giving a bright field of light
used for observing transparent or translucent gem materials
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| observation of a transparent material against a dark background, with illumination fomr the sides rather than from top or below |
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the object is illuminated from above or obliquely
used to observe surface features |
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| inclusions that existed as mineral particles before the host crystal grew |
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| inclusions that formed at the same time as the host material |
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| inclusions that formed after the host material stopped growing |
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