Gravel is one of the most useful forms of stone available. Not only do we use stone for decoration and as a key component in concrete, but it can also be used in paving and a multitude of other landscaping needs.
Knowing the many different types of gravel and what they’re used for can be great way to make the most of any project.
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What is Gravel?
When you think of gravel, you probably picture tiny bits of rock in driveways that get stuck in your shoe. However, gravel is actually defined as a small stone measuring between 3/16 and 3 inches (4.8 to 75 millimeters) in diameter.
They may have round or sharp edges, be smooth or rough, and may be natural or man-made. Stones smaller than 3/16 inches are classified as sands, while those over 3 inches are called rocks.
Note: The terms rock and sand may sometimes be used interchangeably with gravel in relation to the size or a specific type of stone material.
Types of Gravel
1. Aquarium Gravel
Aquarium gravel isn’t just for decoration. This popular fish accessory also serves as a substrate for live or artificial plants and a filter medium. You can purchase aquarium gravel in a number of sizes and either natural or artificial colors, but the ideal size for most fish is 1/8 inches (3mm).
The three best materials to use for aquarium gravel are granite, stone, and iron enriched gravel substrate. You’ll want to avoid painted stones, fine sand, limestone, or any other gravel that might degrade or be accidentally eaten.
2. Bank Gravel
This hybrid ground cover is used to fill low spots in yard or provide a substrate for concrete. It’s made from a mix of large and small natural gravel with sand, dirt, or clay.
Bank gravel not only allows drainage, but helps prevent excess erosion by creating a surface that some plants can take root in.
3. Beach/Creek/River Stone
One of the most popular (and largest) types of gravel, river stone, creek rock, and beach rock are all related forms of natural eroded stone.
They have smooth, often oval-shaped surfaces and may be a variety of greys, tans, and yellows; depending upon the material.
These stones are popular accents in landscaping and are also useful for lining ponds and other water fixtures or as an aesthetic drainage material.
4. Black/Red Lava Stone
This rough stone is (as the name implies) comprised of lava rock. It measures between 1/8 and 2 inches (3.2 to 51mm). The gravels are used as decorative ground cover and borders in gardens.
The red rock, known as scoria, is a popular inorganic mulch for desert-themed gardens, while the black variant is mainly used for its texture.
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Comprising of gravel that ranges from 3/16 to 3/8 inches (4.8 to 9.5mm) in size, chat is the coarse grained leftovers after sifting fine sand.
It’s useful in several construction and landscaping where dust control may be required.
6. Crushed Granite
More commonly known as decomposed granite (DG), these are crushed bits of granite usually harvested from quarries or naturally eroded. The grains measure 3/8 inches (9.5mm) or smaller.
They come as either a natural DG for mulch, a stabilized DG that can be tamped down on a larger gravel substrate to form paths, or in a rein-coated form to create a more natural-looking driveway alternative to asphalt.
7. Crushed Stone
Mechanically crushed stone is another popular form of gravel. The stone used is either limestone or dolomite. Due to the sharp edges of this gravel, it’s most often used as an aggregate for concrete.
8. Pay Dirt
This is a less common form of gravel most commonly harvested when panning for precious minerals. The resulting gravel will often have trace amounts of precious metals such as gold.
It may comprise of any rock type and is rarely used in landscaping or gardening until the valuable materials have been removed. Various types of construction equipment is used to get to and transport pay dirt.
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9. Pea Gravel
Earning its name from the roughly pea-sized (3/8 inch or 9.5 mm and smaller) stones used, pea gravel comprises of both chipped and rounded stone.
Pea gravel is a popular loose aggregate for walkways and driveways. It can also be used in aggregate concrete. Due to the small size, it tends to be both attractive and easy to walk on, making it popular for garden paths or around flower beds or cactus gardens.
10. Crimson Stone
Decorative reddish and burnt orange stones which sometimes have dark gray and black stones mixed in for excellent contrast. Crimson stone is commonly used in garden paths and walkways and will add a unique decorative touch to residential yards and commercial properties.
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There are plenty of other gravel types, most commonly based on a specific rock type. We could go on for hours talking about each one, but here are a few that are worth mentioning for garden use:
- Lag Gravel: This coarse form of gravel is the material left over after sifting finer gravel grains. It tends to be used as a filler material.
- Navajo Sandstone: 3/8 to 3/4 inch natural gravel known for its many mixed colors
- Piedmont Gravel: gravel stones carried and shaped down mountainsides by streams to flat areas
- Slate Gravel: Fine-grain gravel made from crushed slate