Glossary

Alexandrite - one of the world's rarest gemstones, it is a member of the Chrysoberyl mineral family.  It has a natural color change from blue/green in sunlight or fluorescent light to purple/red in incandescent light.   It has a hardness of 8.5 and is the birthstone for the month of June.

AMETHYST - a semi-precious gem from the quartz family.  It comes in all  shades of purple.  It has a hardness of 7 and is the birthstone for February. 

Ametrine - a natural bi-color variety of Quartz.  Part purple amethyst, part yellow citrine.  It has a hardness of 7.

AQUAMARINE - a gemstone from the beryl family.  It is greenish blue and usually rather clear of inclusions.  It has a hardness of 7.5 and is the birthstone for March.

Cabochon - the oldest, simplest style cut of gemstone.  It is round or oval with a plain, curved top surface and best displays the colors and patterns in opaque or translucent stones and optical effects such as sheen, cat's eyes and stars.

CARAT - a unit of weight used for gemstones.  One carat is a fifth of a gram and is divided into 100 points.  Abbreviated ct.  Loose gemstones are usually sold by weight at so much per carat.  Gem density varies with the type of gem material, so stones of the same size may have different weights.

CAT'S EYE - some stones, notably chrysoberyl, contain numerous parallel, needle-like inclusions which, when cut as cabochons, display a cat's eye - a shimmering line along the center length of the stone.

CHERRY OPAL - a type of common opal that is orange-red to deep red.

CHROME DIOPSIDE -  a rare gemstone of brilliant bottle green color - 'green to make an emerald cry.'  Transparent and beautiful green, this calcium magnesium silicate gem makes beautiful jewelry, but is not recommended for the hard wear of a ring, since it has a hardness of only 5.5-6.

CITRINE - a semi-precious gemstone of the quartz family.  It comes in all shades of yellow, gold, rust and brown.  It has a hardness of 7.

CLARITY - the extent of mineral inclusions and flaws in a gemstone.

COLOR CHANGE -  some gemstones appear a different color in daylight than in fluorescent or incandescent light.  Alexandrite goes from green or bluish to purple or red.  Some garnets go from purple to blue.  Some tourmalines change shades of color in different lights as do some sapphires.

Corundum - the mineral family that includes ruby and all colors of Sapphire.  It has a hardness of 9.

CUT - the shape into which a gemstone is faceted such as round, oval, marquise, emerald cut, etc.

DIAMOND -  the hardest of all minerals, diamond also has a fiery brilliance which makes it an exceptional gemstone for jewelry.  Formed under heat and pressure in the Earth from carbon, it is judged by the four 'C's: color, clarity, cut and carat weight.  The most prized is colorless or "white", but diamonds also come in colors.  Most are tinged with yellow or brown, but there are blue, green, black and even red diamonds.    Diamonds have a hardness of 10 and are the birthstone for the month of April.

EMERALD - a gemstone from the beryl family.  Emeralds are many shades of green and few are perfect or flawless.  They easily fracture and do not have the sparkle or 'fire' of diamonds.  They have a hardness of 7.5 and are the birthstone for May.

ENHANCEMENT-  professional treatments applied to gemstones to enhance color (such as heating a ruby); to stabilize a very delicate structure (such as bonding an opal); to enhance clarity (such as lasering flaws in a diamond); to change their color (such as irradiating a topaz to make it blue); to improve general appearance (such as oiling emeralds); or other methods designed to permanently improve the stone.

FACET CUT - a style of gemstone cut using a pattern of highly polished, flat planes, which reflect light and allow light to enter the stone and reflect back up through the top, or table, of the stone from the pavilion, or bottom point.  This displays the gemstone's fire.

FLAW - an inclusion in a gemstone.

GARNET - a family of related gemstones including the silicate minerals almandine, pyrope, spessartine, grossular, andradite, uvarovite, and the green grossular gem tsavorite.  A diverse gemstone group, garnets are best known for their red varieties, but they come in yellow, orange, raspberry, green and even purple.  They have been used in jewelry for over 5000 years. The hardness of garnets is 6.5 - 7.5.    Garnet is the birthstone for the month of January.

HARDNESS - a measure of a gemstone's resistance to abrasion.  The hardest is diamond at 10.

INCLUSION - markings or foreign material incorporated in a crystal as it forms.  Many gemstones have foreign substances within the stone.  These are called flaws or inclusions.

IOLITE - a variety of the mineral cordierite, it is pleochroic - appearing blue in one direction and virtually colorless when viewed from another direction.  It has a hardness of 7 to 7.5.

KARAT - term used to describe the purity of gold.  24 karat gold is pure gold.  14 karat gold is 14 parts gold to 10 parts of other metals alloyed with gold to harden it since pure gold is very soft.

KUNZITE - the pink variety of spodumene.  Easy cleavage makes it quite brittle and not recommended for rings.  It has a hardness of 6 to 7.

LAPIS LAZULI - this semi-precious rock was mined in Persia over 6000 years ago.  Some of these mines are still producing.  It is opaque, mottled, vivid deep blue, and is usually carved or cabochon cut.  It has a hardness of 5.5.

OPAL - opal occurs in two types: precious and common.  Precious opal, (either black or white in color) displays the iridescence usually recognized as opal since Roman times.  Common opal has no iridescence and occurs in a wide range of colors and patterns.  Fire opal is found in colorless to yellow to orange to red tones.  Cherry opal is shades of red.  Sometimes common opal is clear or almost flawless and cut in facets, like fire and cherry opal often are.  Other common opal is cloudy, mottled, or opaque and cut as cabochons.  Some of these are dyed.  It has a hardness of 5.5 to 6.5 and is the birthstone for October. 

PEARL - a gem produced by some aquatic mollusks, especially oysters and mussels.  It is a build-up of calcium carbonate layers and is the alternate birthstone for June.

PERIDOT - a magnesium silicate gemstone that is a member of the olivine mineral group.   Its color ranges from yellowish green to deep olive green and has a hardness of 6.5 - 7.  Peridot is the birthstone for the month of August.

PLEOCHROIC - a term used to describe a gem that has a difference in light absorption when viewed from different directions; thus showing two or more different colors or shades when viewed from different directions.

QUARTZ - one of the most common minerals, it is found in many colors, patterns and optical effects including the transparent gemstones amethyst and citrine; the translucent stones rose and milk quartz; the chatoyant tiger eye and the opaque banded agates.  It has a hardness of 7.

RHODOLITE - a raspberry colored type of garnet.

ROCK - a natural association of minerals both coherent (e.g., granite) and incoherent (e.g. sand).

RUBELLITE - red tourmaline. 

RUBY - one of the world's most valuable gemstones.  It is a member of the corundum family with a hardness of 9.  Different mines produce different shades of red.  Ruby is the birthstone for the month of July.

SAPPHIRE - a very valuable gemstone that comes in a large variety of colors, including clear (or colorless or 'white').  Blue is considered to be the most desirable color.  Sapphire is a corundum stone, has a hardness of 9, and is used extensively in fine jewelry.  Sapphire is the birthstone for the month of September.

SPINEL - a clear gemstone of magnesium aluminum oxide, spinel may have other minerals replacing the aluminum which produce many colors.  Pure spinel is colorless, but it is found in reds, pinks, greens and blues.  The reds have been mistaken for ruby; the colorless have been used like diamonds.  Spinel has a hardness of 8.

STAR - a four point or six point star is displayed in a cabochon cut stone when mineral inclusions and structures within the stone are lined up in such a way that the reflection of light from them causes a display of two or three shimmering lines that intersect to form a star.  Sapphires form stars.

TANZANITE - a rare variety of the mineral zoisite that is blue with a violet tinge.  It has a hardness of 6.5.

TOPAZ - an aluminum silicate gemstone that is found in many shades of blue also colorless, and shades of yellow, orange, brown and pink.  Topaz is the birthstone for November and has a hardness of 8.

TOURMALINE - a borosilicate mineral that varies greatly in its composition and has the greatest color range of any gemstone.  It is strongly pleochroic, the strongest color occurring along the length of its long, slim crystals.  It has a hardness of 8.

TSAVORITE - a rare green grossular garnet found at Tsavo in Kenya.

TURQUOISE -  this semi-precious stone was one of the first gems to be mined in Sinai over 6000 years ago.  It is a phosphate mineral that is an opaque sky blue color due to its copper content.  Iron gives some turquoise a greenish tint.  It is porous and rather soft at a hardness of 5-6.  It is usually carved or cabochon cut and is the alternate birthstone for December. 

ZIRCON - a natural, mined stone, that comes in many colors including blue, green, clear (colorless or 'white') and earth tone shades of yellow, gold and brown.  It has a hardness of 6 to 7.5.  Its luster and fire rival that of diamonds.  Blue Zircon is the birthstone for the month of December.

 

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