GIA GG flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- GIA color scale
- D to Z scale grading diamond bodycolor against masterstones, from colorless (D–F) through near colorless (G–J) to light yellow or brown (S–Z).
- Flawless clarity
- A clarity grade meaning no inclusions or blemishes are visible at 10x magnification, judged under controlled lighting on the loose stone.
- Internally Flawless
- A clarity grade with no internal inclusions at 10x but surface blemishes permitted; it sits just below Flawless on the GIA scale.
- Cut grade components
- Brightness, fire, scintillation, weight ratio, durability, polish, and symmetry combine into the cut grade for D–Z round brilliant diamonds.
- Carat conversion
- One carat equals 0.20 grams, 200 milligrams, or 100 points; price per carat rises disproportionately with size because large rough is rare.
- Diamond fluorescence
- Emission under UV light graded None to Very Strong, usually blue; strong fluorescence can sometimes give a hazy appearance.
- Hue, tone, saturation
- Three descriptors of colored stone color: hue is spectral position, tone is lightness to darkness, saturation is intensity from grayish to vivid.
- Clarity Type I
- Colored stones that are usually eye clean in nature, such as aquamarine and topaz; inclusions are less expected and penalized more.
- Clarity Type III
- Colored stones that are almost always included, such as emerald and red beryl; grading is more lenient than for Type I stones.
- Asterism
- A star effect seen in some corundum caused by oriented rutile inclusions reflecting light into intersecting bands on the surface.
- Play-of-color
- A phenomenon in opal where light diffracts through silica spheres, producing shifting spectral flashes as the stone is viewed from different angles.
- Alexandrite color change
- A hue shift from green in daylight to red under incandescent light, caused by trace chromium absorption in the chrysoberyl structure.
- Refractive index
- A measure of how much light bends entering a gem, read on a refractometer; birefringent stones show a range between two values.
- Birefringence
- The difference between a gem's high and low refractive indices; diagnostic values include quartz 0.009, corundum 0.008, and zircon 0.059.
- Specific gravity formula
- SG equals weight in air divided by the difference between weight in air and weight in water, measured with a hydrostatic balance.
- Pleochroism
- The display of different colors in different crystal directions, observed with a dichroscope and used to distinguish anisotropic gems of similar color.
- Curved striae
- Growth lines that curve, visible under magnification; they suggest a flame-fusion synthetic rather than a natural gem with straight growth.
- Cubic zirconia properties
- A common diamond simulant with RI near 2.176, SG around 5.6–6.0, and strong dispersion; it is singly refractive and shows no doubling.
- Moissanite properties
- A diamond simulant with RI near 2.65–2.69 and strong birefringence; doubling of facet edges is visible under magnification.
- Pearl luster
- The sharpness and brightness of reflections on a pearl surface, graded excellent to poor; it is the most important appearance factor in grading.
- Pearl shape categories
- Round, near-round, oval, button, drop, baroque, and circled; round pearls command the highest premium within a type.
- Nacre thickness
- The layer of nacre deposited over a nucleus or tissue; thin nacre reduces durability and can crack or reveal the bead.
- Tahitian pearl color
- Bodycolor ranges from light gray to black, often with green, peacock, or aubergine overtones; these saltwater pearls are usually bead-nucleated.
- Akoya overtones
- Cultured saltwater pearls typically white or cream with pink, green, or silver overtones; they are bead-nucleated and usually round.
- Imitation pearl test
- Imitation pearls are coated beads with uniform surfaces and no drill-hole irregularities; magnification and the tooth test help distinguish them.
- Gold karat purity
- 24k is pure gold; 18k is 75 percent, 14k is 58.3 percent, and 10k is 41.7 percent gold by weight in the alloy.
- Sterling silver
- An alloy of 92.5 percent silver and 7.5 percent other metals, usually copper, marked 925 for purity.
- Prong setting
- Metal claws that hold a gem and expose much of its surface to light; it maximizes brilliance but leaves the stone more exposed to damage.
- Bezel setting
- A metal rim encircling the gem's girdle; it protects the stone well and is suited to softer stones and active wear.
- Pavé setting
- Many small stones set closely with tiny beads of metal between them, creating a continuous surface of sparkle.
- Feature-benefit selling
- Linking a product attribute, such as a secure bezel setting, to a customer benefit, such as durability for everyday wear.
- Treatment disclosure
- The ethical and often legal requirement to tell customers about treatments, synthetics, and simulants affecting a gem's value and care.