Long ago, I gave my younger brother Fred — who now has a doctorate in geology — a small piece of teardrop-shaped labradorite I’d picked up from a rock shop on holiday. Later, he told me that my gift had prompted the beginning of his interest in geoscience.
“Look over there,” said Fred on a recent walk along the beach, “That’s a huge piece of old magma.”
Sure enough, an obvious volcanic intrusion about the size of a sheep stuck out of the sand like a sore thumb. It’d been there since the Palaeogene period about 66 million years ago, when a volcano — later the isle of Arran — about 18 miles east of us erupted with great enthusiasm.
I strode over to a large red sandstone boulder, itself a piece of 275-million-year-old fossilized Permian desert, and contemplated the scene.
The black volcanic scoria sat in sharp contrast to the rest of the rocks on the beach. About a hundred yards to my left, seals slept on a jagged outcrop made of olivine diabase. In front of me lay a collection of multicolored stones, brought to the beach by longshore drift. Granite, flint, limestone and quartzite, sitting on top of the pale sand. So much history in such a small space.
Rocks are fascinating. Look at the side of a box canyon and you’ll see all of history sandwiched into ancient sedimentary deposits. In other places, little pieces of obsidian and pumice in the soil speak of billion-year-old volcanos, long extinct. Then there are earth tone river pebbles, polished smooth as they tumble from source to delta.
Rock collecting isn’t hard to get into — and every new rock you collect marks the beginning of a journey of discovery. Other rock collecting hobbyists, friendly geologists and comprehensive books can help you identify the specimens you collect.
Before you dive into your brand new rock-collecting hobby, you’ll need to learn a little about geology. It’s fascinating — and a bit of basic knowledge can help you identify the specimens you bring home.
Feldspar, schist, granite, pumice — there are lots of different named rock varieties on planet Earth, and they all fall into one of three categories: igneous, sedimentary and metamorphic. Each main type has defining characteristics, which you can use to narrow down your rock ID.
Igneous rocks have fiery origins: they’re formed when magma or lava cools and solidifies. Some igneous rocks — like granite and olivine diabase — have a coarse-grained crystalline structure, so they sparkle in the sunlight. Others, like obsidian and the scoria I mentioned earlier, have a fine-grained crystalline structure, so they look dull.
Sedimentary rocks are some of the easiest rocks to identify: they’re quite soft in comparison to metamorphic rocks, and they’re made of multiple layers of material. Sediment layers are deposited underwater, by glacial action, or by the wind. Most fossils are found in sedimentary rock or low-grade metamorphic rock. Flint, limestone and sandstone are all sedimentary rocks.
As the name suggests, metamorphic rock represents geological metamorphosis. When igneous or sedimentary rocks are subjected to a lot of pressure and heat inside the Earth’s crust — when they’re sandwiched and “baked” between layers of molten rock, or buried under developing mountain ranges, for instance — they change structure. Sedimentary rocks like shale become slate, quartz-rich sandstone becomes quartzite, and siltstone becomes pelite.
Rocks are made of mineral crystals — and sometimes, those crystals are big enough to see with the naked eye. Take the quartz or amethyst crystals on the inside of a geode, for instance. Occasionally, large quartz, feldspar, garnet or other mineral veins develop between layers of igneous or metamorphic rock.
Some minerals are brightly colored, while others are radioactive or magnetic. Some are hard; others are soft and crumble between your fingers.
Researching Local Geology
Researching your local geology — or the geology of the area you plan to collect rocks in — can help you decide where to look for specimens. You’ll find helpful interactive geological maps of America at the United States Geological Survey (USGS) website, which you can zoom into to see surface geology details. Just click on a colored zone to learn more about the rocks in that area.
If you want to conduct more in-depth research, check out the National Geologic Map Database. Some museums also include exhibits about local or regional geology.
What You’ll Need
You don’t need a lot of equipment to begin collecting rocks. Most novice rockhounds start with the following things:
- Geological pick. Extract softer clay and shale specimens with a geological pick.
- Geological hammer. Split harder rocks — including small geodes — with a 16 ounce geological hammer.
- Geological chisel. Break rocks and geodes precisely with a hammer and a chisel.
- Pry bar. A pry bar can help you loosen specimens and move large rocks out of the way.
- Crack hammer. Use a 3 or 4 pound crack hammer to break off larger pieces of rock.
- Brush. This can be a large, soft-bristled paintbrush or a toothbrush — or both. Brushes help you clean rocks on the go.
- Magnifying glass. Take a closer look at your samples with a magnifying glass
- Safety glasses. Protect your eyes from rock splinters and dust with a decent pair of safety glasses.
- Collecting bags, newspaper and a pen. Pack sharp rock specimens in newspaper or wrapping paper. Bag specimens and label them to keep track of where they came from.
- Field bag. You’ll need a field bag to put everything in. Choose a bag with wide straps to avoid straining your shoulders.
Other useful items include a pocket-sized field guide, a trowel, a penknife, a bucket and a larger crowbar. Smartphone apps like Smart Geology- Mineral Guide, Geology Rocks – Handbook of Rocks or Rock Identifier: Stone ID also come in handy. You’ll develop your own list of favorite tools as you gain experience.
Make sure you wear appropriate clothing when you go rock collecting. You’ll probably need sturdy walking boots, heavy-duty cargo pants or jeans, and close-fitting gloves. If you plan to visit a potentially unstable site, always wear a hard hat.
Where to Find Rocks
Rocks are everywhere. Dig down deep enough and you’ll find a layer of bedrock under the soil in your backyard. If you’re not sure where to start gathering specimens for your collection, lift a piece of lawn turf, or investigate the loam in your garden.
After that, look for places where rocks have been exposed by human activity. Active and abandoned quarries, mines, excavation sites and construction sites, for instance, all have great rock-hunting potential. You’ll need permission before going on private property, and you might need to wear protective equipment — a hard hat, or a high-visibility jacket, for example.
Other excellent rock-collecting sites include beaches, river beds, rocky exposures and outcrops, and cuttings.
- Beaches and river beds. Harder igneous or metamorphic rocks are more resistant to the weathering action of water, so they’re more common than sedimentary rocks on beaches and in river beds. Because they tumble in from many different locations, beach rocks are generally called “rocks without context.” River rocks, on the other hand, are likely to be local.
- Rocky exposures, outcrops and cuttings. Also known as “living rock,” exposed bedrock can tell you a lot about the geology of an area. Road cuts, or cuttings, provide excellent insight — especially when they’re new. If cuttings are on public land, you won’t need permission to use your tools.
Which Rocks to Collect
See a rock you like? Great — pick it up, and add it to your collection. There are no rules about which rocks to collect and which to leave behind. Rocks don’t have to be pretty or unusual to be interesting.
Many people began their rock collections with specimens they find fascinating — like the piece of labradorite I mentioned at the beginning of this guide. Some hounds collect rocks in rainbow colors, while others focus on specific mineral types. You could collect a piece of rock from every state, or a sample from every country in the world. It’s really up to you.
After a while, your rock collection will probably get quite large. Maybe you’ll gravitate toward one or two particular specimen types — septarian nodules, ores or silicates, for instance; perhaps you’ll decide to collect as many different kinds of rock as possible.
Cataloging Your Rock Collection
Cataloging is an important part of rock collecting. Most rock collectors use one of the following two methods to catalog the rocks they find:
- The baggie method. Put your rock in a clear plastic bag and label the bag with a code or number.
- The white paint method. Apply a spot of white paint to your rock, wait for it to dry, and write your number or code directly on the rock.
Until recently, many collectors wrote catalog notes on index cards, or in notebooks. Field journals remain essential, but most modern amateur geologists also use computers to log data. Some rockhounds create spreadsheets, while others catalog their collections using programs like Trilobase or NM Collector. Whatever you decide to do, include the following information about each specimen in your records:
- Code number (what you wrote on the rock, or on the bag)
- Collection date
- Type of rock
- Chemical formula
- Size and weight
- Where the sample came from
- Other interesting notes
Ethical Rock Collecting 101
You have a 16-ounce geological hammer in your field bag and you’re not afraid to use it. Not so fast, rockhound — before you get stuck into the nearest outcrop, brush up on a few geology ethics. You’ll build goodwill with landowners and help preserve the natural environment if you follow these ethical rules:
- Ask permission. Always ask before venturing onto private property.
- Respect the law. Get familiar with federal laws, state laws and local rules and regulations about rock collecting.
- Don’t detonate. Don’t use explosives or firearms to break up bedrock.
- Don’t damage. Don’t cause any damage to your rock-collecting site.
- Don’t contaminate. Don’t dump anything in streams, rivers and other on-site water supplies.
- Don’t be greedy. Don’t take too many rocks.
- Stay tidy. Leave your site as you found it — clean up, close gates and take your litter with you.
- Extinguish fires. Don’t light fires unless you absolutely have to. If you do light a fire, make sure it’s fully extinguished before you leave.
- Cooperate. Communicate and cooperate with colleagues and group leaders.
- Report unusual findings. If you dig up fossils, find archeological remains or unearth suspected meteorites, tell local authorities right away.
A Rocky Conclusion
If you’re interested in geology, rock collecting might be your ideal hobby. It doesn’t cost much to get started, and you can prime your collection with specimens from your backyard — or from your local beach. You’ll learn all about the history of the planet as you go along, and after a while, you’ll be able to identify different types of bedrock on sight. Eventually, you’ll be a seasoned amateur geologist — and then you can help other enthusiasts become rockhounds.