One of the most enjoyable ways to rockhound is taking a stroll along the coast, looking for interesting beach rocks. You never know what you might find! The beach is one of the best hunting grounds for treasures like petrified wood, fossils, agates, and jasper.
The most common rocks to find on the beach are igneous rhyolites, basalt, gabbro, granite, dolerite, obsidian, and pumice; sedimentary dolomite rock, conglomerate, and sandstone; metamorphic rocks like milky quartz, chert, chalcedony, amethyst, slate, smokey quartz, and rocks with quartz veining.
The types of rock on different beaches around the world depend on the geological and geomorphological history of a particular area. That is part of what makes beach rocks so interesting – they are clues to the history of the landscape. By learning about how different types of rocks form, and how to identify different minerals one can have fascinating beach rockhounding experiences.
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Beach Rocks are Mysterious
Geologists refer to beach rocks as ‘stones with no context’. This is because it is difficult to tell where a beach rock could have come from.
It may have tumbled down a cliff and made its way onto the beach, or it could be from a rocky outcrop or reef deep in the ocean. Maybe it traveled from hundreds of miles inland and was deposited on the beach at the mouth of a river.
Beach rocks have a certain mystery to them. One needs to play detective to try and guess the origin of the rocks. By knowing the characteristics of different rock types, and how to identify them, we can figure out the origin of beach stones and pebbles.
Types of Beach Rocks
All rocks, including those found on the beach, are categorized into three different types, based on their geological origin: igneous, sedimentary, and metamorphic. By understanding the various rock types, one can learn to identify stones and pebbles on the beach.
Deep inside Earth’s crust, high temperatures melt rock, forming magma. When a volcano erupts, it spews magma, and as it flows and cools, it recrystallizes into minerals we refer to as igneous rocks. Examples of igneous rocks are basalt, pumice, and granite.
The surface of the Earth constantly gets weathered and eroded by the forces of water and wind. The particles of sediment that are freed from rocks accumulate, compact, and over time form sedimentary rocks. Larger pebbles, chips of rock, and cobbles accumulate to form a conglomerate. Organic matter from plants and animals can settle in the sediment and lithify, forming fossils. Examples of sedimentary rocks are breccia, shale, sandstone, and limestone.
Metamorphic rocks form when extreme heat and pressure deep under the Earth’s surface transforms rocks, changing the original form and crystalline structure. Examples of metamorphic rocks are slate, marble, quartzite, and gneiss.
What are the Most Common Beach Rocks?
Some beaches are covered in millions of stones and pebbles, while other beaches are sandy with only a handful of stones. The types of rocks found on a beach depending on the geology of the area and what geomorphic processes are at play.
Rocks found on the beach are usually smooth and rounded because they have been tumbled and polished over time by the motion of the waves.
These are the 25 most common rocks to come across on beaches around the world:
Agates are a form of microcrystalline quartz. Agate is characteristically banded with beautiful translucent stripes and fine grain. They can be white, gray, blue, red, or orange.
TIP: Agates are beautiful rocks but they can be even more beautiful when polishing them. Do you know how to do it? Find out a simple step-by-step guide on how to cut and polish agates in the article below:
Basalt is a dark-colored igneous rock that makes up most of the ocean floor. Basalt is fine grained, and on the surface, there are tiny holes – remnants of when gas bubbles escaped the cooling lava. Sometimes basalt rocks are veined with quartz. It can be reddish-brown to black in color.
Chalcedony is similar to agate in that it is a microcrystalline quartz. Chalcedony is translucent, with a dull, waxy luster, and can be colorless, white, gray, or blue in color.
Conglomerates are sedimentary rocks that are composed of various shapes and sizes of rounded stones, cemented together by sand and pebbles. They are easily identified because there are clear fragments in a matrix. They are sometimes called ‘pudding stones’. Man-made conglomerates from building rubble are common to find on beaches.
- Diabase, or dolerite
Diabase, or dolerite, is a dark-colored rock that is similar to basalt and gabbro. It has a slightly coarser texture than basalt but has fewer visible crystals than gabbro. These are found as well-worn cobbles or boulders. Colors vary from black to gray, green-black, and brown.
Diorite is a pegmatite rock that is composed mainly of feldspar and other dark-colored minerals. They have a black and white salt and pepper pattern. It is similar to granite but has a finer grain.
Dolomite rock, a sedimentary rock, is often confused with limestone because it shares many of the same characteristics. A lot of dolomites formed during the Cambrian Period, as large amounts of calcium carbonate from coral, shell, and algae accumulated in shallow marine environments. The Dolomites come in all shapes and sizes, from boulders to pebbles. They can be slightly pink, green, white, yellowish, purple, gray, or even black.
Fossils are surprisingly common to find at the beach. They are usually embedded in cliffs and rockfaces. These are concrete type fossils. Look on the beach for round rocks that have white stripes or markings. Using a pick, break the stones. The inside may be a shell, shark tooth, or bone.
Gabbro is an igneous rock that is similar to basalt, but it forms when magma cools very slowly in the Earth’s crust. It is dark gray or black, and shiny where bits of feldspar are visible.
TIP: Gabbro is one of the most common rocks you can find in oceans. But do you know other rocks or gemstones come from the ocean? Find out more in the article below:
Geodes are hollow rocks that contain crystals. Without breaking one open, it is difficult to tell if a rock is a geode. Look for organic-shaped rocks that are not angular or narrow. Tap it on a hard surface, it makes a hollow sound.
Granite, an igneous rock, is composed of mica, quartz, feldspar, and hornblende minerals. Granites come in a great variety of forms. They can be identified by the visible crystals of white or gray quartz, black mica, and pink feldspar. Another defining feature is that granite has no horizontal banding.
Jasper is a quarzitic mineral that has beautiful patterns and colors. It can be mottled, striped, or spotted, and varies from yellow and tan to red, brown, and even green (rare).
Limestone, a sedimentary rock that is composed mainly of calcite, is white or grey in color with a chalky texture. Limestone forms over millions of years from the aggregation of shells and skeletons of marine creatures.
Marble is a metamorphic rock that is composed of recrystallized calcite. It is a medium to coarse grained rock that is light in color. Upon closer inspection, crystals of calcite may be visible, and when held up to the light and slowly turned, the crystals sparkle.
Obsidian, an igneous rock, forms when lava cools very rapidly. It is shiny, smooth, and black.
- Petrified wood
Petrified wood is wood that has fossilized. If wood is covered by sediment, it does not decay because it is not exposed to oxygen. Instead, mineral-rich groundwater flows through the sediment, and over millions of years the minerals from the water, like silica, calcite, and pyrite replace the original wood. This forms a wooden fossil that still bears the pattern of the wood and bark.
TIP: Did you find petrified wood on your rockhounding trip and what to know how valuable it can be? The value of petrified wood depends on various factors, find out more in the article below:
Pumice, an igneous rock, forms when magma is super viscous, trapping tiny bubbles of gas as it cools. The frothy lava domes solidify into a lightweight, light-colored, pitted, or spongy-looking pumice.
Quartz is the most plentiful mineral on the planet, so you are sure to find some at the beach. It comes in many different forms and colors due to inclusions. For example, red quartz is stained by iron and amethyst contains iron and aluminum. Milky quartz looks white and opaque at first glance but holds it up to the light and you will see its translucence.
Rhyolite is an igneous rock that is rich in silica. It is often red, brown, gray, or pinkish. Because it forms from magma that cools fast, it has a fine grain and can exhibit banding, or have darker streaks.
Sandstone is a sedimentary rock that forms when eroded particles of quartz and feldspar accumulate, become compacted, and cemented together over time. Sandstone can be coarse grained to very fine grained, depending on the parent rock, and it can be beige or gray in color.
- Sea Glass
Sea Glass is the result of the manmade glass being tumbled by the ocean, turning smooth and frosty. Sea glass, or mermaid tears, are highly sought-after collectibles. Many pieces have been in the ocean for 20-50 years. The most common colors to find are white, green, light blue, and brown. Rarer colors are yellow, red, and purple.
Serpentine rocks can be found in various shades of green. They can also be yellow, black, or white. With a waxy luster, serpentine rocks have a slippery feel when you hold them, similar to a snake.
Siltstone is a sedimentary rock composed of silt that has hardened through heat and pressure over time. It has a fine grain with no laminations. Siltstones vary in color from red to brown, to gray, and black.
Slate is a metamorphic rock that is composed mainly of clay minerals. It forms when shale buried deep under the ground is transformed by heat and pressure. It is very dark in color, either dark gray or black and it has a very fine grain. There are distinct layers that are visible and it feels smooth to the touch.
Syenite is a gorgeously colorful rock, with a medium to coarse grain. Syenite is an igneous rock, similar to granite, except it does not contain quartz. It is composed mainly of feldspar, and its color varies depending on what minerals it contains. It varies from light pink to orange.
How to Find Beach Rocks
Choose the right time to go rockhounding on the beach. The best time of day is during low tide. During high tide, the sea brings in new material, and as the tide goes out, they are deposited on the beach. The movement of the tide can also uncover rocks that were buried.
It is best to go when there are not many people at the beach – early spring and winter are good seasons to look for beach rocks. However, the beach can be cold at this time of year, so wear warm, waterproof, and wind-resistant clothing, gloves, waterproof boots, and a hat.
When beachcombing for rocks, the angle of the sun is important, as it makes some stones, like agates, easier to see. Ensure that the sun is in front of you.
TIP: Did you know you can make money for a living by selling rocks and minerals? Find out how to start and what to focus on in the article below:
Where to Find Beach Rocks
Stones, cobbles, and pebbles can be found on almost all beaches around the world, so finding beach rocks is as simple as heading to your local beach and looking around.
Look along the waterline and the rocky shore, check at the base of big dunes, and search higher up on the beach, above the high-water mark.
Do some research online as there are many rockhounding groups on Facebook and Reddit that share beaches that are great for finding minerals and rocks. Join local geology or rockhounding group to get the best local knowledge about rockhounding beaches in your area or nearby.
Here is the list of rockhounding guides for the US states with the best beaches for rockhounding:
- All About Rockhounding in Oregon: Where to Go & What to Find
- Where to Go Rockhounding in Washington State & What to Find!
- The 9 Best Places to Dig for Gems in California (with maps)
- Rock Hunting in Michigan: Best Locations & What You Can Find
- Where to Rockhound in Florida (and What You Can Find)
Rocks found on the beach are all smooth and rounded because they have been tumbled and abraded by the sand and waves. It is difficult to determine the origin of beach rocks because they could have been transported long distances.
One can commonly find all three types of rock at the beach: igneous, sedimentary, and metamorphic. The most common beach rocks are agates, basalt, conglomerate, granite, slate, rhyolite, and quartzite. However, this will largely depend on what beach you visit.
The types of rocks found at a particular beach depend on the underlying geology of the area. Some beaches have endless boulders, stones, cobbles, and pebbles, while others only have a few.
BTW: Do you want to know more about rocks and minerals identification? The books listed below are the best ones you can find on the internet (Amazon links):
- The Crystal Bible
- Smithsonian Handbooks: Rocks & Minerals
- Gemstone & Crystal Properties (Quick Study Home)
- Ultimate Explorer Field Guide: Rocks and Minerals (National Geographic Kids)
The best time for beach rockhounding is in early spring and winter when there are few other people on the beach. Go to the beach at low tide, as this is when you are most likely to find treasures that have been washed in by the tide.
Find beach rocks by searching the entire length of the beach systematically, starting with the most likely places to find rocks – at the base of large dunes, above the high-water mark, and along the waterline. Walk with the sun in front of you so that it is easier to see translucent rocks.
TIP: Beach rocks are often naturally tumbled but what to do in case you want to tumble your rocks by yourself? Check out the best rock tumblers for beginners and hobbyists in the article below:
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