When thinking of the colorful world around us, rock colors probably don’t come to mind. First, we think of plants and animals, especially flowers and birds. The stereotype is that rocks are just gray or brown, but if you look at a variety of rocks, you’ll see that they’re much more beautiful than most people give them credit for.
So, what colors can rocks be, and how do they get those unique colors? There’s more to rocks than meets the eye.
What Colors Can Rocks Be?
Rocks can be almost any color, depending on the type of rocks and where you find them. You probably won’t see a purple rock laying outside your home, but they can exist in more secluded areas of the world.
The most common rock colors are black, gray, brown, red, and green. Of course, you’ll find lots of variations of these colors, such as tan, dark brown, or rust, depending on where you look.
What Defines a Rock?
When you picture a rock, you probably think of a round, gray object outside. Yet, the specific definition is “a naturally occurring solid mass.” They’re made of mineral materials, such as granite, sand, and clay.
Not all rocks are made of the same materials, which is why there’s such a wide variety of rock appearances. A stone differs from a rock because it’s simply a piece of rock that has been polished.
What Determines a Rock’s Color?
Several factors can determine a rock’s color. The chemical composition, weight, and environment can all play a role in the rock’s appearance. So, here are a few things that can make a rock look the way it does.
The minerals that make up rocks are the biggest factor in determining their color. A rock will inherit colors from some of the minerals, and the minerals with the highest amounts will be predominant. That’s why there are so many colorful minerals and stones on our planet.
If a mineral is 100% pure, it will be a single color. For example, calcite is always white on its own. For a mineral’s color to vary, it would have to have an impurity. An impurity occurs when foreign elements become part of the mineral’s structure. So, if iron comes into contact with quartz, the color may shift.
Minerals can get impurities in many ways, but a common method is through water. When stones rest in water, there may be traces of other elements in the water. That’s why when some rocks rub against objects, they’ll develop rust-like edges as a result of interacting with iron.
Stones and rocks are made of a combination of minerals, which is why they have so many color options. So, the minerals that are in a rock will influence what it looks like.
For example, rocks containing iron may appear red. Rocks with high amounts of titanium or magnesium might look black, while rocks with a high concentration of aluminum or silicon may be light-colored instead.
Aluminum is an almost colorless mineral, so when it’s part of a rock, it lightens the color. Other colorless or very lightly colored minerals are sodium and potassium. White, light gray, light yellow, and light pink are common colors for rocks with these elements.
Here’s an overview of what mineral colors you might expect:
- Iron – Dark red or brown
- Chromium – Dark green
- Copper – Blue or green
- Manganese and cobalt – Pink
- Uranium oxides – Yellow or green
Unique Mineral Combinations
Some minerals overpower the other ones they’re combined with, such as chlorite, which can turn a mineral combination from white to green. So, the combination of minerals matters just as much as the individual elements.
Here are a few examples of colors associated with chemical compositions:
- Fe2O3 – Dark red
- Cr − Ni − Co – Light orange
- As – Yellow
- Cr2O3 − MgO – Blue
Even if two rocks have a mineral material in common, they can be completely different colors based on the other minerals involved. Thus, the minerals inside a rock have the biggest impact on its color.
Weight and Gravity
A rock’s weight can also influence its appearance, which goes hand-in-hand with the elements inside it. Light-colored minerals, such as silicon and aluminum, are usually lighter in weight too. Dark-colored minerals, like iron and magnesium, are often heavier. Thus, if you hold a light-colored rock and a dark-colored one of the same size, you might notice that the dark-colored one weighs a little more.
Colors can vary based on the three main types of rocks: sedimentary, igneous, and metamorphic. Each type is formed in different environments as a result of different external materials, which can play a role in how the rock looks.
Sedimentary rocks are created by an accumulation of particles from the Earth’s surface. A rock is made when all these parts settle into place. The environment and the amount of oxygen during sedimentation can create rocks made of different colors.
Here’s an overview of what color the environment and oxygen can create:
- Deep, stagnant water with no oxygen – Black
- Shallow, circulating water with a little oxygen – Gray or green
- Terrestrial with a lot of oxygen – Brown or red
Black, gray, and green colors can also be associated with decaying plant matter, while brown and red could be a sign of iron rusting.
In general, darker-colored rocks were formed in areas with low oxygen and lighter colors are formed when more oxygen is present. That’s because rocks with low oxygen cannot support certain bacteria that are linked to lighter colors. More oxygen allows the microorganisms to break down into organic matter when the rock is formed.
Igneous rocks are formed at high temperatures from the magma trapped inside the Earth. They usually aren’t as colorful, but they can be both light and dark colors. Shades of gray are the most common.
Even though magma is associated with red, igneous rocks can’t be red or similar colors because iron minerals won’t oxidize in that type of environment.
Metamorphic rocks are made from pre-existing rocks that are exposed to heat, pressure, fluids, or other factors. Thus, they usually inherit the colors of the rocks they were made from, so there aren’t any specific rules for how they get their appearances.
Rock Color Meanings
All the colors in the world around us can have some meaning to them. If you enjoy collecting rocks, you might have a color preference based on the symbolism behind it. The meanings of rock colors are similar to crystal color meanings.
Gray Rock Meaning
Gray is the color most people picture rocks as. It might seem dull, but it’s seen as a color of balance since gray is a combination of black and white. It symbolizes compromise, practicality, and neutrality. Some consider it a sign of wisdom since hair turns gray with age. However, others see the color as a lack of emotion.
Black Rock Meaning
Some people associate the color black with darkness, but it’s more commonly a symbol of protection. It’s a color that’s powerful, elegant, and sophisticated. People wearing black outfits are often seen as professional and mysterious, which is why black rocks are often intriguing.
Brown Rock Meaning
Brown rocks are the same color as the dirt beneath them, so they’re a sign of stability, reliability, and comfort. They’re a symbol of structure, and they can signify growth like the roots in the ground. However, some associate this simple color with being boring and predictable.
Red Rock Meaning
Red objects evoke strong emotions, which is why you might feel compelled to pick up a red rock. It’s a color of strength and courage but also love and passion. Extroverts are most commonly drawn to the color red because of its energetic appearance. In negative situations, red could symbolize anger or danger.
White Rock Meaning
White stones showcase purity, peace, and compassion. People associate it with light, ghosts, death, and old age. The meaning can vary greatly depending on the culture. Rocks that appear transparent share similar meanings to white.
Orange Rock Meaning
The color orange falls perfectly between red and yellow, so it takes some meanings from both. It’s seen as rebirth or a “breath of life.” It still has lots of energy, but it’s not as overwhelming as red. It can also symbolize friendship, enthusiasm, and curiosity.
Green Rock Meaning
Most people associate the color green with nature, so the same is true for green rocks. With that in mind, it can mean growth, youth, life, and harmony. Yet, darker green colors are sometimes viewed negatively because they’re seen as a sign of jealousy. Yellow-green is often viewed as a sickly color.
Blue Rock Meaning
It’s unlikely that you’ll come across blue rocks on your daily walk, but blue is another color associated with nature. It’s related to oceans, sleep, and twilight. Many people view blue as a calming and supportive color, while it can also be a sign of loyalty and trust.
Yellow Rock Meaning
Yellow rocks represent the sun, warmth, and gold. The color is often perceived as a symbol of energy, joy, and wisdom. In rare situations, it could be seen as a bad thing, such as fear or jealousy. Light or bright yellow are viewed positively, while dark yellow is more haunting.
Purple Rock Meaning
Purple rocks are probably the most uncommon color, but they exist in certain situations. Since purple is a rare color in nature, it’s seen as a color of magic and royalty. It’s also a symbol of tranquility, so people may feel peaceful while admiring purple stones.
Several factors can cause a rock to become the color it is, but the main reason is the chemical composition. All minerals have unique colors, and when they’re combined to make rocks, they develop a unique appearance.
So, next time you look at a pretty rock, you’ll have some idea as to how it got its color. If the appearance and meaning resonate with you, it might be time to start a rock collection.