Why Are Gemstones Different Colors?

Written By Allie Perry September 13, 2024

If I showed you a red stone and blue stone and asked you to tell me which was the ruby and which was the sapphire, could you do it?  Both of those stones are classics, so I bet you could.

But what if I told you they were the same thing?

You might think I'm bonkers, but technically they are the same thing! (And fine, some days I am bonkers, so you’d be a little bit right, too.)

How about amethyst and citrine? One is purple and one is a yellow-orange, but they’re also the same thing!

One of the most fascinating aspects of gemstones is their diversity of colors. These colors are often the result of subtle differences in their chemical makeup, so while we might think of gemstones like amethyst and citrine as completely different, they both just varieties of quartz, altered by slight changes in their composition. Similarly, rubies and sapphires are both forms of corundum, colored differently by trace elements.

Quartz: Amethyst and Citrine – Different Colors, Same Family

Quartz is one of the most common minerals on Earth, and it comes in many colors. Two of the most well-known varieties are amethyst (purple) and citrine (yellow to orange). While they may appear quite different, both are part of the quartz family, with their colors resulting from tiny differences in their chemical composition.

1. Amethyst (Purple Quartz)

• Color: Amethyst gets its signature purple hue from trace amounts of iron and irradiation. When quartz contains iron impurities and is exposed to natural radiation within the Earth, the iron atoms take on a specific charge that causes the crystal to absorb light differently, resulting in its deep violet color.
• Formation: Amethyst can vary from pale lavender to deep, royal purple. The depth of the color is influenced by the amount of iron present and the level of radiation the stone has experienced.

2. Citrine (Yellow Quartz)

• Color: Citrine owes its yellow to orange color to heat treatment. In nature, citrine is relatively rare, and many citrines on the market are actually amethysts or smoky quartz that have been heated to create a yellow hue. When quartz is heated, either naturally or through artificial means, the iron impurities rearrange, changing the way the crystal absorbs light and resulting in the warm colors we associate with citrine.

3. Amethyst and Citrine Together: These two stones can even appear together in a single crystal, known as ametrine, where part of the quartz remains purple while the other part has been transformed into yellow or orange.

Corundum: Rubies and Sapphires – A Rainbow from the Same Mineral

Rubies and sapphires might seem like entirely different gemstones, but they are both varieties of the mineral corundum, one of the hardest materials on Earth. The difference in their colors comes down to the trace elements found in the crystal.

1. Rubies (Red Corundum) 

• Color: Rubies are prized for their deep red color, which comes from the presence of chromium within the corundum crystal. The chromium absorbs certain wavelengths of light, giving the stone its intense red hue.
• Quality: The finest rubies are referred to as pigeon’s blood rubies, which exhibit a rich, vivid red with a slight blue undertone. 

2. Sapphires (Blue Corundum)

• Color: While sapphires are most commonly associated with blue, they can occur in a wide range of colors, including pink, yellow, and green. Blue sapphires get their color from trace amounts of iron and titanium within the corundum. When these elements are present in the right amounts, they cause the crystal to absorb light in such a way that the blue hues are emphasized.
• Fancy Sapphires: Sapphires that aren’t blue are often called fancy sapphires, and they can range from pink sapphires (colored by chromium) to yellow sapphires (colored by iron). This variety of colors makes sapphires incredibly versatile gemstones.

Other Gemstones That Come in Multiple Colors

1. Tourmaline

•  Color Variety: Tourmaline is one of the most colorful gemstones, with shades ranging from pink, green, blue, and even multi-colored stones like watermelon tourmaline, which has pink centers and green edges like a slice of watermelon.
• Chemistry: Tourmaline’s color is influenced by a complex array of elements. For example, iron and titanium can cause blue or green hues, while manganese can create pink or red tourmaline.

2. Garnet 

• Color Variety: While garnets are often thought of as deep red, they come in nearly every color except blue. Green garnet (called tsavorite) is one of the rarest and most prized varieties.
• Chemistry: Garnet’s color changes are due to different elements within its structure. Almandine garnets (red) contain iron and aluminum, while spessartine garnets (orange) contain manganese.

3. Spinel

• Color Variety: Spinel is another gemstone that comes in a wide range of colors, from red to blue, pink, and even purple.
• Chemistry: The red variety of spinel gets its color from chromium, similar to rubies, while iron imparts blue and purple hues.

Why Do Gemstones Have Different Colors?

The color of a gemstone is primarily influenced by trace elements within its crystal structure. When light interacts with the atoms in the gemstone, certain wavelengths of light are absorbed, while others are reflected, creating the colors we see. Here's a breakdown of how this works:

1. Chromium: Often responsible for red, pink, and orange hues, chromium is the element behind the color in rubies and certain sapphires.
2. Iron: Commonly produces green, yellow, or blue tones. Iron plays a key role in the colors of citrine, green tourmaline, and sapphires.
3. Titanium: This element helps create blue hues, as seen in blue sapphires and blue tourmaline.
4. Manganese: Produces pink, red, and orange colors, as found in pink tourmaline and spessartine garnets.

How Chemistry Affects Durability and Value

The trace elements that give gemstones their colors can also affect their durability and value. For example:

• Chromium-rich rubies are highly sought after, but too much chromium can make the stone brittle.
• Heat treatments can improve color but may decrease the value if the stone is heavily treated.
• Tourmaline’s value often depends on the saturation of its color, with deep, rich hues being more valuable than lighter tones.

So whether you did great in high school chemistry or you had to get your friend’s older sister to tutor you so you didn’t flunk it, the beautiful spectrum of color gemstones display is all due to chemical composition!

And even if you never remember the science behind gemstone colors, if “gemstones” is ever a category at pub trivia, you’ll be able to sit back and gleefully enjoy your cheese fries because you’ll have this category in the bag!

I like to make jewelry with stones in all colors, and you can click here to see it all!