There are many types of gemstones in the world, all of different gem families, colors, and hardnesses. Gem hardness is rated on the Mohs scale of hardness, which assigns numbers from 1 to 10, with 10 representing the hardest. The intervals between the values are not equal. The numbers for a gemstone can vary depending on the exact make up of a particular stone. The test uses scratching for the basis of hardness. A harder mineral will scratch a softer one, but not the other way around. Hardness is not an indication of toughness or strength. Hard minerals can be brittle. Knowing the hardness of your gemstones can help you care for them.

A gemstone with a hardness of:

  • 1-2 can be scratched by a fingernail
  • 3 can be scratched by a copper coin
  • 4-5 can be scratched by a knife
  • 6-8 can scratch glass
  • 9-10 can cut glass

 

Alexandrite

Alexandrite is a rare variety of the mineral Chrysoberyl. In outdoor light it looks bluish green, and in indoor light it has a more purplish-red color. It has a hardness of 8.5-9 on the Mohs scale.

Amethyst

Amethyst is a purple gemstone that is part of the Quartz family. Its purple color can range from cool bluish purple to deep reddish purple, the latter being considered gem quality. Amethyst has a hardness of 7 on the Mohs scale.

Black Opal

Black Opals are part of the Opal family, and are generally considered to be the most valuable of all the varieties which include White Opal, Boulder Opal, and Mexican Fire Opal. Black Opal has a darkish grey color. It has a hardness of 5-6.5 on the Mohs scale.

Blue Sapphire

Part of the Corundum family, Blue Sapphires are valued based on the purity of their primary hue. A secondary hue of violet or purple can positively affect the color of the Sapphire, while a secondary hue of green is considered negative. Sapphires have a hardness of 9 on the Mohs scale.

Blue Star Sapphire

Star Sapphires are Sapphires that are heavily included with rutile, causing a star-like reflection that is most visible when the stone is cut in a cabochon shape.

Citrine

Citrine is a member of the Quartz family, and generally has a yellowish or orange color. It has a hardness of 7 on the Mohs scale.

Denim Blue Sapphire

This is a Blue Sapphire with a light clear blue color, rather than the traditional deeper and richer blue.

Emerald

High quality Emeralds that are mostly free of inclusions can be used in rings, but most Emeralds on the market are of low quality, full of cracks and fractures which makes them more susceptible to breaking and therefore unsuitable for most jewelry. Emeralds have a hardness of 7.5-8 on the Mohs scale.

Golden Sapphire

Yellow and Golden Sapphires are another variety of the Corundum family, also a 9 on the Mohs scale.

Mint Tourmaline

Mint Tourmalines are one of many varieties of the Tourmaline family. Tourmalines come out of the ground in all sorts of colors, sometimes at once in the bi-color and multi-color varieties. They have a hardness of 7-7.5 on the Mohs scale.

Morganite

Morganite is part of the Beryl family, which makes it a cousin of the Emerald and Aquamarine gemstones. It has a delicate pink color and was named after J.P. Morgan, an avid gem collector. Morganite has a hardness of 7.5-8 on the Mohs scale.

Orange Sapphire

Orange Sapphires are another variety of the Corundum family, also a 9 on the Mohs scale.

Peach Sapphire

Peach Sapphires, which can be of a more yellow or more pink type of color, are another variety of the Corundum family. Also a 9 on the Mohs scale.

Peridot

Peridot is a lime-green colored stone that has a hardness of 6.5-7 on the Mohs scale.

Pink Sapphire

Pink Sapphires are another variety of the Corundum family, also a 9 on the Mohs scale.

Ruby

Ruby is also part of the Corundum family. It can be found in a range of red hues, from purplish to orangish. Only red Corundum are considered to be Rubies. All other colors of Corundum are called Sapphire. Ruby has a hardness of 9 on the Mohs scale.

Spessartite

Spessarite is part of the Garnet family and can be found in orange and brown colors. It has a hardness of 6.5-7.5 on the Mohs scale.

Tanzanite

Tanzanite is a purple gemstone that is mined exclusively in Tanzania. It has a hardness of 6-7 on the Mohs scale.

Topaz

Topaz is a gemstone that ranges in color from gold to pink to orange to brown. It has a hardness of 8 on the Mohs scale.

Tsavorite

Tsavorite is another member of the Garnet family, and it has a transparent and usually intense green color. It has a hardness of 7-7.5 on the Mohs scale.