Tutorials
There is so much to understand about fine jewelry and precious gemstones. Loretta wants her visitors to know a little more about the definitions of gemstone terms so that one's experience on this site and with other gem and jewelry research is a richer experience.
Our brief tutorial here is certainly not exhaustive. But we hope it adds to every jewelry lovers' knowledge base, and clarifies some terminology associated in this wonderful avocation.
Binocular Microscope
A critical piece of magnifying equipment in a professional laboratory. The gemological microscope has twin objectives & oculars which provides three dimensional viewing, various magnification lens, plus variable illumination sources to examine the exterior and interior of an object.
Branded Gemstone or Diamond
A proprietary, often patented gemstone cut making the stone recognizable as a unique shape. Branded cut stones may also bear identifying laser inscriptions on the girdle (circumference).
Carat Weight
A measure of weight, rather than the size of a gemstone or diamond as expressed by carats.
Certificate
A written report describing the results of examination of a gemstone, diamond or other valuables detailing the weight, proportions, color and clarity grades, and any other variables pertaining to its identity and quality.
Clarity Grade
A method of expressing relative levels of clarity in a diamond. Gemological Institute of America (GIA) has developed the most widely accepted grading scale ranging from highest, Flawless (FL) to Included 3rd level (I3), or lowest.
GIA Clarity Grading: FL-IF-VVS1-VVS2-VS1-VS2-SI1-SI2-I1-I2-I3.
Color Grading Scale (GIA)
Colorless diamonds are graded on a scale beginning with the letter D and continue to the end of the alphabet.
| D-E-F | Colorless |
| G-H-I-J | Near Colorless |
| K-L-M | Faint Yellow |
| N O-P-Q R | Very Light Yellow |
| S-T-U -V-W-X-Y-Z | Light Yellow |
Diamond
A unique gem-mineral composed essentially of only one element: carbon. It is the hardest of all known natural substances ranking10 on the Mohs scale. It occurs in colorless form, called "white" diamonds, but also occurs naturally in a wide range of colors.
Dispersion
The term used to express a transparent gem or diamond's ability to separate white light into the spectral colors; also referred to as fire.
Facet
A polished surface placed on a diamond or gem.
Face-up Color
Apparent color observed in a diamond or gem viewed in a direction perpendicular to the table or how it would appear in its setting.
Fancy Cut
Any gemstone shape or cutting style other than a Round Brilliant cut. This includes pear, heart, emerald cut, marquise, princess, trillion, cushion etc.
Fancy Color
A diamond with an attractive natural body color other than very light yellow. This includes pink, blue, brown, fancy yellow (canary) and other rare colors. Any color sapphire other than blue is called Fancy Color sapphire.
Flaw
A catch-all term referring to any internal or external characteristics on a cut diamond or gemstone, also called imperfections or inclusions.
Flawless (Fl)
A diamond or gem with no internal or external flaws or blemishes when viewed under 10X magnification.
Four Cs
An easy to remember quality assessment for diamonds: Carat weight, Color, Clarity and Cut.
Full Cut (or Brilliant Cut)
A round cut diamond with the total of 58 facets.
Gem
A cut and polished stone that possesses the necessary rarity, beauty, utility and durability for use in jewelry or for a collection.
Gem Identification
A series of systematic tests performed in a laboratory or other setting as allowed until an absolute separation (identification) is made of the stone in question.
Gemology
The science and study of all issues relating to gemstones including their identification, description, origin, and grading.
Graduate Gemologist or GG
One who holds a Graduate Gemologist Diploma from the Gemological Institute of America (GIA).
Gram
The weight in grams of metal used in jewelry or decorative items. 28.35 grams = 1 ounce Avoirdupois
Hardness
A relative ranking of a mineral's resistance to being scratched. The Mohs scale developed in the 19th century is the most accepted method for comparison of relative hardness. Diamond, the hardest known substance is rated 10 on the Mohs scale, and talc is the least hard mineral, ranking 1 on the Mohs scale.
Imperfection
Any internal or external flaw or blemish on a polished diamond or gemstone, also called an inclusion.
Karat
A measure of gold purity or fineness, usually stamped on a piece of jewelry with the mark K or KT after a number. It represents the relationship of pure gold to the total metal alloy. 24K means pure gold. 14K equals 58.5% pure gold in the total metal.
Loupe
A handheld 10X optical device, corrected for spherical & chromatic aberration used for examining gemstones.
Microscope
See Binocular Microscope
Millimeter (mm)
Metric system unit of 1mm = 0.001 meter. 6 mm measures nearly 1/4 inch.
Mohs Scale
See Hardness
Polariscope
An optical instrument used to identify a gemstone as having single or double light refraction; one of several tests used in gemstone identification.
Refraction
This is how a gemstone handles light rays entering it, and is expressed in a stones' RI or Refractive Index.
Refractive Index (R.I.)
A measurement of how light rays change direction (related to speed) as they enter or exit a gemstone. There is a direct correlation between the higher RI's and a stones' brilliance.
Refractometer
An optical instrument used in the laboratory for measuring the refractive index of a gemstone.
Specific Gravity
A way to measure and articulate the relative density of gemstones to that of water.
Ultraviolet Light
Electromagnetic wave lengths shorter than that of visible light. The use of ultraviolet light is important in the study of diamonds and colored gems because of the (identifying) fluorescent effects seen in some gems.
