Jewelry Education – Gem Guide
The hardness of each gemstone below is based on a gem-trade standard called the Mohs scale. The higher the Mohs scale number, the harder the stone is. The highest Mohs scale rating is 10, diamonds. Anything with a Mohs scale rating of less than 7 is easily scratched.
Mohs’ scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. It was created, in 1812, by the German mineralogist Friedrich Mohs and is one of several definitions of hardness in materials science.
Alexandrite
Alexandrite is the birthstone for June (along with the Pearl) and the anniversary gem for the 55th year of marriage. It changes from green to red, mauve or brown in incandescent light. Alexandrite has a hardness rating of 8.5. There are many synthetic alexandrites on the market. Natural alexandrite is very rare. Alexandrite is found in Brazil, Madagascar, Myanmar, Russia, Sri Lanka and Zimbabwe.
Amethyst
Amethyst is the birthstone for February and the anniversary gem for the 6th year of marriage. It is purple quartz and one of the most popular gemstones. It varies from pale lavender to deep purple with red highlights. Amethyst is generally abundant and quite inexpensive. It has a hardness of 7.
Aquamarine
Aquamarine is the birthstone for March and the anniversary gem for the 19th year of marriage. It is light blue, blue-green and dark blue. It has a hardness of 7.5. Aquamarine often becomes paler if left out in the sun.
Citrine
Citrine is the birthstone for November (along with Topaz) and is the anniversary gem for the 13th year of marriage. It is yellow to brown quartz. It varies from pale yellow to rich golden yellow to dark orange. Darker colors are more highly prized, including medium golden orange (“Rio Grande” citrine) and dark sherry-colored (“Madeira” citrine).
Diamonds
Diamonds are the birthstone for April and the anniversary gem for the 10th and 60th years of marriage. They can be slightly yellowish, and in this general color range, but those most approaching absolute lack of color are most prized. However, brightly colored diamonds are much rarer and more expensive. It has a hardness of 10.
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