You may have heard “river rock” being thrown around in landscaping circles as of late, as it’s becoming a rather popular decorative choice of residential yard design, but, if you’re anything like me, you find the term infuriatingly nondescript.
River rock is a rather nebulous pair of buzz words referring to a quasi-family of rocks rather than any one stone in particular. But what then are these sibling stones that make up the river rock tribe?
This is exactly what I wanted to find out, so I did some digging, and here’s what I managed to unearth!
River Rocks — Bonded By Experience, Not Blood
As we assumed, river rocks is an umbrella term that refers to rocks that have experienced certain weathering due to similar geographical positions, i.e. in rivers, stream beds, and beaches…. Basically anywhere there are both rocks and flowing water.
This pseudo group of rocks is incredibly diverse due to the fact that each location capable of producing them may have a completely different catalog of native rocks.
What Do River Rocks Look Like?
They come in a variety of sizes, but those used for landscaping purposes are typically small- to medium-sized, and due to the eroding massage of water over time, they tend to be relatively flat and smooth with rounded edges.
They often feature various cracks, pits and imperfections, yet more evidence of their historical proximity to flowing water, and their color can be as varied as their size.
Which Of The Three Major Rock Types Make Up The River Rock Family?
The river rock family can be composed of igneous, sedimentary, and metamorphic rock formations; it all just depends on the geography of their watery resting place.
For instance, if the stones in question are found in the Waihee River in Hawaii, there’s a good chance that most are igneous rocks, as there are 15 volcanoes scattered around The Aloha State.
What Are The Most Common River Rocks
Although the list of possible river rocks is technically endless, as there is no agreed total of specific rock types, and any of them could wind up in a moving body of water, there are a few considered to be the most common.
Granite
Not just a popular choice for our kitchen countertops, granite is the most common type of river rock, and makes up a significant amount of the Earth’s continental crust.
In light of this, it’s really no surprise that this rock winds up in rivers and streams all the time, as water erosion is constantly digging deeper into the ground.
An igneous rock formation, it’s derived from magma and is composed primarily of alkali metal oxides and silica (quartz).
The color of granite can vary, but perhaps the most arresting examples are purple or green, with more commonplace finds being black, white, or gray.
Basalt
The high augite and pyroxene content of basalt provides its signature black or gray hue, and much like granite, it’s a volcanic rock. Basalt is particularly prevalent in northern Nevada, western Idaho, and eastern Washington and Oregon.
Schist
Schist is metamorphic, coarse-grained rock composed primarily of mudstone and shale; however, it will often exhibit interleaves of quartz and feldspar.
There are a number of varieties named for the type of rock found inside it, for example, you can get tourmaline schist, garnet schist, and mica schist.
In fact, this stone commonly plays host to precious gemstones such as rubies and sapphires, so next time you’re having a riverside walk, perhaps it’ll be worth taking a dip and cracking a few of these bad boys open!
Limestone
If you’re more of a fossil hunter than a treasure hunter, forget about schist and make a beeline for the limestone!
50% of this intriguing formation consists of ancient marine deposits (calcium carbonate), meaning they’re often teeming with fossils and sometimes even sparkly geodes!
This white, gray, yellow, blue, orange, brown, violet, or black rock is easily eroded by the motion of water, which is why there are astounding cave-like limestone formations across the globe.
Shale
A fine-grained sedimentary rock common to floodplains and river deltas, shale is formed when silt and mud fuse together, creating shelves made up of delicate segments of lamination.
Final Thoughts
There you have it — River rock is an umbrella term used to refer to any rocks that have been uniformly weathered by extended exposure to moving water.
Hypothetically, any rock on the planet could wind up a river rock, but the most common of all include granite, basalt, schist, limestone, and shale.