Color is undoubtedly the most important criteria for evaluating and selecting gem varieties. Because gemstones come in a rainbow of shades, therefore color grading can be very complex. The three key criteria experts look at are hue, tone, and saturation. These attributes combine to create the colors we observe in stones. Lighting is another important factor; gemstone color and brilliance can appear very different depending on the light source.
Major factors that determine color of a gemstone
The hue of a gemstone is its base color. Hue can combine to produce additional hues in precious stones, such as orangish-red, yellow orange, yellow green, green blue,or violet blue. The Gemological Institute of America (GIA) has developed a list of 31 hues for describing gemstones: 7 base hues and 24 combination hues. Gemstones with a single pure hue tend to be the most highly valued.
Tone describes the lightness to darkness of a gem color. A pink gemstone, for instance, might be categorized as “light pink” or “medium pink”. The GIA tone scale has a total of 11 points, going from colorless to black.
Saturation is the intensity or purity of a color. With lower saturation, gemstone color becomes less pure and a gray or brown hue can be seen. The most desirable gem variety is those with strong saturation and even color throughout.
According to the GIA saturation scale, there are six degrees of saturation, ranging from grayish or brownish to vivid. As saturation decreases, gemstones with cool hues can appear grayish, while gemstones with warm hues can appear brownish.
Gemstones by color
Star Ruby, Beryl, Red Diamond, Malaya Garnet, Star Garnet, Almandine Garnet, Pyrope Garnet, Rhodolite Garnet, Amber, Fire Opal, Tourmaline, red coral, red Spinel, Imperial Topaz, Sunstone, red Tourmaline, red Zircon
Emerald, Green Garnets: Tsavorite and Demantoid Garnet, Chrome Diopside, Jadeite, Green Sapphire, Green Chrome Tourmaline, Bloodstone, Green Diamond, Green Chrysoberyl, Green Beryl
Blue Green / Blue Gemstones
Sapphire, Blue Tourmaline, Blue Tanzanite, Iolite, Flourite, Aquamarine, Blue Opal, Blue Spinel, Turquoise, Lapis Lazuli, Blue Zircon
Violet or Purple Gemstones
Amethyst, Garnet, Topaz, purple or violet Sapphire, Iolite, Tanzanite, Purple Diamonds, Purple Chalcedony, Purple Spinel, Purple Jade, Purple Fluorite, Purple Kunzite, Purple Tourmaline.
Rose Quartz, Star Ruby, Rhodonite, Rubellite, Pink Tourmaline, Pink Opal, Pink Fluorite, Kunzite, Morganite, Star Garnet, and Pink Spinel.
Orange Diamond, Orange Sapphire, Orange Zircon, Imperial Topaz, Oregon Sunstone, Spessartite Garnet, Mexican Fire Opal, Orange Spinel, Amber, Helidor, Spinel, Tourmaline, Quartz, Sapphire.
Obsidian, Black Tourmaline, Black Onyx, Tahitian Pearl, Black Opal, Schorl Tourmaline
Citrine, yellow Sapphire, Topaz, yellow Tourmaline, Transparent Opal, yellow andradite garnet, spessartine and Mali Garnets, yellow Beryl, Sphene, yellow Zircon, Spodumene and transparent varieties of Labradorite and Orthoclase Feldspar.
White Gemstones or Colorless Gemstones
Diamonds, White Sapphire, White Topaz, White Agate, Pearls, White Opals, White Jade, White Jasper.
Multicolor Gemstones & Colorful Gemstones
Multicolor Agate, multicolor ammolite, Multicolor andalusite, Multicolor black opal, Multicolor bloodstone, Multicolor cat’s eye opal, Multicolor chocolate opal, Multicolor chrysocolla, multicolor color change diaspore, Multicolor color change fluorite, Multicolor color change garnet, untreated multicolor color change sapphires, Multicolor coral, Multicolor dendritic agate, Multicolor fire agate, Multicolor fluorite, Multicolor hawk’s eye gemstones, Multicolor labradorite, Multicolor mystic quartz , Multicolor mystic topaz, Rainbow pyrite, Multicolor rhodochrosite, Multicolor ruby-zoisite.