The most common question we get from the Rock Chasing community is “can you identify my rock?”. If you’ve sent this question to us yourself don’t be embarrassed, it’s a great question!
If you’ve ever stumbled upon a unique rock or mineral and wondered about its name or origin, you’re in the right place. With the right knowledge and tools, it’s entirely possible to identify your rock, even if you’re just starting out.
Each rock has its own set of unique characteristics, much like a fingerprint. Color can be an initial clue; some minerals have a consistent hue while others vary widely.
The way a rock shines or doesn’t, known as its luster, offers another hint. Then there’s the hardness. Some rocks can easily scratch glass, while others might crumble if you try.
As you dive into this guide, you’ll learn more about these characteristics and how they can help identify what rock or mineral you have in your hand.
The Key Points When Identifying Rocks
There are several very important things you need to know or find out if you want to make an accurate rock identification. You don’t need to know them all but the more you know the easier it will be.
Where your rock was found
One of the most helpful things you can know about a rock or mineral you are trying to identify is where it was found. That tends to really narrow down the possibilities very quickly.
While some rocks are found all over the planet, most tend to be found in specific areas. To help you narrow down the options, we’ve put together state-by-state guides below that cover many of the common and rare rocks you can find:
Rock and mineral guides for each state
*Click On Each State To See The Full Guide*
You can also click on the links below to see the rock and mineral guide for each state. We cover a lot of examples that can be helpful when you’re trying to narrow down the rock you’ve found from a list of possibilities.
Color – Some minerals display a range of colors, while others have consistent shades
Color is the light that bounces off an object and enters our eyes, letting us see different shades and hues.
When identifying a rock or mineral, observing its color is a great first step. Some minerals always show up in certain colors, making them easy to spot. For example, malachite is always green.
However, be cautious! Some rocks and minerals can come in various colors. For instance, quartz can be clear, pink, or even purple. So, while color is a helpful clue, it’s best to combine it with other identification methods.
How to determine or use color to identify a rock
To use color for identification, first clean your rock or mineral with water and gently dry it. In good natural light, inspect the color closely. It’s helpful to have a rock and mineral guidebook or an online resource handy.
These guides often categorize rocks and minerals by color, making it easier to narrow down what you have.
For example, if you see a bright blue mineral, it could be turquoise or azurite. By matching your observation with pictures and descriptions in the guide, you’ll be on your way to pinpointing its identity.
Type – Various rock types have clear differences
Rocks are grouped into three main families based on how they’re formed: igneous, sedimentary, and metamorphic.
These rocks come from cooling lava or magma. Think of a volcano erupting with hot, molten rock. Once that liquid rock cools down and solidifies, you get igneous rocks!
Examples include granite and basalt. They can form above or below the Earth’s surface.
Formed layer by layer, sedimentary rocks are made from bits of other rocks, plants, or shells. Over time, these bits gather in places like lakes or oceans.
Pressure packs them together into rocks like limestone or sandstone. Sometimes, you might even see fossils in them!
Metamorphic rocks: These are rocks that have changed. Starting as either igneous or sedimentary, they transform due to heat and pressure inside the Earth.
A great example is marble, which starts as limestone and then changes with a bit of Earth’s cooking!
How to determine rocks according to their type
Igneous rocks can have sparkly minerals like quartz. If your rock has layered or banded patterns, it might be metamorphic. Sedimentary rocks, meanwhile, can have layers that look like pages in a book.
Knowing the rock type helps because some minerals are mostly found in one type. For example, olivine is common in igneous rocks. With this info, you can match your rock or mineral with guides to narrow down its name.
Streak – Minerals can have different apparent colors but a consistent streak
In the world of geology, the streak of a mineral is the color it leaves behind when it’s rubbed against a rough surface, like a white unglazed tile. It’s kind of like when you use chalk on a blackboard.
Even if the mineral’s outer color changes due to impurities, its streak usually remains consistent.
To identify a mineral using its streak, you simply scrape or rub it on an unglazed tile, which is often called a streak plate. The color that appears can give you a big clue.
A mineral’s streak is like its secret message to help you figure out what it is!
How to determine or use a streak to identify a rock
Even if the mineral itself is sparkly or colorful, its streak might be a totally different color!
For example, while pyrite (fool’s gold) is shiny gold, its streak is greenish black. And while hematite can look silver, gray, or red, it leaves a reddish-brown streak.
By comparing the streak color to a mineral guide, you can more easily identify rocks.
Luster – Different minerals reflect light in different ways
Luster describes the specific way a rock or mineral reflects light. It’s like how some things are super shiny, while others have a softer glow.
There are different types of luster. For example, minerals with a metallic luster shine like metal. Some minerals might have a glassy luster, shining like a piece of glass.
Identifying a rock or mineral based on its luster is fun and simple. Just hold it under a light and observe how it shines. The way it reflects light can give big hints about what it is.
How to determine or use luster to identify a rock
When you pick up a rock or mineral, tilt it under a light or in the sunshine. Notice how the light bounces off it. Does it sparkle a lot or just a little?
By paying attention to how shiny or dull it is, you can match its luster with known descriptions from rock and mineral guides. So, next time you find a cool rock or mineral, let its luster give you hints about its identity.
Clarity – The transparency of minerals is a crucial factor in rock identification
In geology, clarity talks about how clear a mineral is and how well you can see through it. Some minerals let light pass through them easily, while others might be cloudy or completely opaque.
There are a few terms we use to describe clarity. If a mineral lets all light through and you can see through it clearly, it’s called transparent. When it allows some light but you can’t see details clearly, that’s translucent.
And if no light passes through, it’s opaque.
How to determine or use clarity to identify a rock
If you hold a mineral up to a light source and see straight through it, it has high clarity. If it’s somewhere in the middle, not clear but not totally dark, we call that translucent. If no light gets through, it’s opaque.
Knowing the clarity can help in identification. For instance, many gemstones like quartz can be super clear, while others like turquoise are opaque.
Grain Shape and Size – Rocks and minerals have different grain shapes and sizes
When you look closely at a rock, especially with a magnifying glass, you’ll notice it’s made up of tiny bits called grains.
These grains can be round, jagged, flat, or even needle-like. Their shape can give clues about the rock’s history.
Grains can be super tiny, like sand on a beach, or much bigger, like pebbles in a riverbed. The size of these grains can tell you a lot about where and how the rock formed.
How to determine or use grain shape and size to identify a rock
Closely examine a rock and try to see how big the grains are. Are they tiny like sugar? Or big like little pebbles?
Next, see if the grans are smooth and rounded or if they have sharp edges. Some rocks, like sandstone, have tiny, round grains. Others, like granite, have a mix of sizes and shapes.
If a rock has big, rounded grains, it might have been tumbled in water. But if it has sharp, tiny grains, it might have formed in a place with less movement.
Hardness – The Mohs hardness scale can help identify your rock
Hardness tells us how tough or soft a mineral is. Think of it like this: some minerals are as tough as a diamond, while others can be as soft as a piece of chalk.
There’s a scale called the Mohs scale that ranks minerals from 1 (softest) to 10 (hardest). Talc is super soft, so it’s a 1. Diamond is the hardest, so it’s a 10.
How to determine or use hardness to identify a rock
To test the hardness, you can try scratching the mineral with a common item like your fingernail, a copper penny, or a steel nail.
Minerals have different hardness levels. If your mineral can be scratched by your fingernail, it’s pretty soft. But if it needs something harder, like a steel nail, to leave a mark, it’s quite tough!
By knowing the hardness of a mineral, and comparing it to a chart or a book, you can get a big clue about its identity.
Some Additional Ways To Identify Your Rock
There are a few more ways of identification worth noting. Some of these may require some more specialized equipment but they can be very reliable:
Crystal Structure – Different minerals form in specific crystal shapes
Crystal structure is like the secret blueprint of minerals! Every mineral grows in a certain pattern that repeats over and over, forming its crystal structure. These structures can look like cubes, needles, plates, or other cool shapes.
Each mineral has its own unique crystal structure. For example, salt (or halite) often forms in neat little cubes. On the other hand, quartz has a hexagonal, or six-sided, shape.
How to determine or use crystal structure to identify a rock
To see the crystal structure, sometimes you just need to look closely at a mineral. You might see flat surfaces, edges, and angles that give away its pattern.
Other times, you may need to break the mineral to see a fresh, clean surface. Comparing the shapes and patterns you see with pictures in a rock and mineral guide can help with rock identification.
Cleavage – Some rocks and minerals have smooth breaks, others don’t
Cleavage in the world of rocks and minerals is super fascinating! It describes the way a mineral breaks. Instead of breaking randomly, some minerals split along smooth, flat surfaces. Others might not have cleavage at all.
This happens because of how the mineral’s atoms are arranged.
Each mineral with cleavage will break in its own special way. For instance, some might split into flat sheets, while others might break into blocky chunks.
How to determine or use cleavage to identify a rock
To spot cleavage, take a close look at your rock or mineral. See if there are any flat surfaces that look like they’ve been sliced perfectly.
Count how many different directions those flat breaks happen in. For example, some minerals might break in one direction, like sheets of paper, while others might break in two or more directions.
By noticing these breaks and comparing them to a rock and mineral guide, you can get a big clue about the identity of your rock!
Chemical Composition – Each type of rock is defined by its elements
The chemical composition of rocks and minerals is basically their recipe! Every rock or mineral is made up of certain elements, and these elements mix together in specific ways.
It’s just like how a cake needs flour, sugar, and eggs. In the same way, a mineral like quartz is made up of silicon and oxygen.
Some minerals, like diamonds, might be mostly made of one element. Meanwhile, others have a mix of different elements.
How to determine or use chemical composition to identify a rock
To find out the chemical composition of a rock or mineral, scientists often use special tools in labs.
But for rock enthusiasts, we can sometimes make good guesses based on color, where it’s found, or how it reacts to certain tests, like whether it fizzes in vinegar.
When you have a rock or mineral, compare its features with what’s known about different compositions. This can help you narrow down what you’ve got in your hand.
Density – High-density minerals tend to feel heavier than they appear
In simple terms, density tells us how much stuff (or mass) is packed into a certain space. Some rocks might feel heavier than others of the same size because they have more density.
To figure out a rock or mineral’s density, you’d compare its weight to its volume. For instance, gold is super dense. That’s why a small piece of gold feels heavy.
Think of it like this: if you have a small object that feels super heavy, it has a high density. But if that same-sized object feels light, it has a low density.
How to determine or use density to identify a rock
To get an idea of a rock or mineral’s density, you can compare it to something you know. For example, if you have a piece of quartz and a piece of lead the same size, the lead will feel much heavier.
That’s because lead has a higher density than quartz.
Many rock and mineral guidebooks list the density of different types. So, if you’re curious about a rock or mineral you found, check its weight and size, and then look up its density in a guidebook.
Matching the density with the list can help you figure out what you have!
Formation – Rocks and minerals form through various geological processes
Minerals form in unique ways, and that can give us big hints about what they are! For example, if a mineral comes from cooling magma, it might be sparkly like quartz or dark like basalt.
Minerals that form when water evaporates, like in a shallow sea or a dried-up lake, can include things like halite, which is just table salt!
And then there’s the heat and pressure method deep in the Earth. This can turn one mineral into another, making minerals like garnet or mica.
How to determine or use formation to identify a rock
Now, knowing how a mineral forms can help identify it. If you find a mineral in a place where there was once a lot of heat, like near a now-dormant volcano, it might have come from cooled magma.
Minerals in areas that were once underwater might have formed from evaporating water. And those found deep underground or in mountain areas? They could’ve been made by the heat and pressure.
Magnetism – Magnetism in rocks and minerals is a useful trait when trying to identify rocks
Magnetism is a super cool force that some rocks and minerals have! It’s like an invisible pull that can attract certain metals or even other magnetic rocks.
Just like how a fridge magnet sticks to your refrigerator, some rocks have this magnetic pull too.
One famous magnetic mineral is magnetite. If you ever find a rock that attracts metal or sticks to a magnet, there’s a good chance that it’s magnetite.
How to determine or use magnetism to identify a rock
To check if a rock or mineral is magnetic, you just need a simple magnet from your home. Hold the magnet close to the rock or mineral. If it gets pulled towards the magnet or sticks to it, that means it has magnetism.
Discovering magnetism can be a big hint in narrowing down what you have. Not all rocks or minerals are magnetic, but when you find one that is, it’s a fun and clear sign of its identity.
Fluorescence – Only certain kinds of rocks and minerals glow under UV light
Fluorescence is like a surprise party for some rocks and minerals! When certain rocks and minerals are exposed to ultraviolet (UV) light, they glow in amazing colors.
It’s similar to how some clothes or posters shine bright under black lights at a bowling alley.
Some minerals, like fluorite, are known for this glowing trick. They might look ordinary in daylight, but under UV light, they reveal their bright and colorful side.
How to determine or use fluorescence to identify a rock
To see if a rock or mineral is fluorescent, you need a UV light. Simply shine the UV light on it in a dark room and watch for any glowing colors. Not all rocks and minerals will glow, but the ones that do can give clues about their identity.
For example, certain types of calcite will glow red or pink under UV light. If you find a rock or mineral that glows, it’s a fun and helpful way to get closer to figuring out what you have.
Conductivity – Most rocks aren’t conductive, but some are
Conductivity is a neat property that tells us if a rock or mineral can let electricity flow through it. Think of it like a highway for electricity. Some rocks and minerals have open highways, letting electricity zoom through, while others have roadblocks.
A common mineral known for great conductivity is copper. That’s why we often use it in wires and electronics!
Knowing if a rock or mineral is conductive can help identify it. For instance, if a mineral looks metallic and is also conductive, it might be a metal like copper or silver.
On the other hand, most non-metallic minerals won’t be conductive.
How to determine or use conductivity to identify a rock
To test a rock or mineral’s conductivity, scientists use a simple tool called a conductivity meter. When the probes touch the rock or mineral, the meter will show if electricity can pass through.
You probably don’t have a conductivity meter lying around at home, but you can ask a gemologist to help you identify your rock with the help of more advanced tools.