emeralds

Pretty green gem-quality crystals

Chemical Composition of Gemstones

Here’s a neat infographic from Compound Interest (one of my favorite websites) that describes 16 different gemstones and why they have different colors. It also includes their chemical formulas and hardness on the Mohs scale.

Many gemstones would be colorless or a different color if not for the presence of small amounts of transition metals such as chromium or titanium. For example, you can see that aquamarine and emerald both have the same chemical formula Be3Al2(SiO3)6, but emeralds are green because of chromium ions replacing some of the aluminum ions and aquamarines are blue because of iron 2+ or 3+ ions replacing some of the aluminum ions. Click through to read the whole article, because there are many other ways that gems and minerals get their colors!

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Emeralds

Emeralds are the most famous green gemstone. The word emerald is practically synonymous with the color green, and in fact, the name emerald comes from the Greek smaragdos which means “green gem.” Ireland’s nickname “The Emerald Isle” sadly does not refer to any emeralds found there but for the green scenery.

Emeralds are the green variety of the mineral beryl. The famed green color comes from chromium impurities. When beryl appears in other colors due to different impurities it is called aquamarine (blue), morganite (pink), bixbite/red beryl (red), or heliodor (yellow). Emerald rates 7.5-8.0 on the Mohs hardness scale, though it can be brittle. Emeralds are usually found in Colombia (South America) or Zambia (Africa) in granite pegmatites and metamorphosed mica schists. They grow in hexagonal crystals. The most valuable emeralds for gems are transparent rather than opaque, have few inclusions, and are a dark shade of green. Emeralds usually have quite a lot of inclusions, so sometimes people use oil to hide them, but looking at the inclusions can help you tell where the emerald came from. One final fun fact: There is even a faceting method called the emerald cut, which has a rectangular face with 8 sides. It is also known as the octagon cut. The emerald cut works well on emeralds but can be used on any gemstone, even diamonds.