Why is dirt almost always a brown color?


Why is dirt almost always a brown color?

In: 329

You know rust? Those orange-brown crumbs that form on things made of iron if they‘re left in a humid environment for too long? Earth‘s crust contains a lot of iron and the same thing happens with the iron that‘s in the environment. It then spreads everywhere and mixes with other stuff in the environment, but that other stuff is often colorless (white, gray, black), so the brown tone from the iron is what‘s determining the color.

A few elements are more common in earth‘s crust than iron (for example: silicon and aluminium), but stuff that contains those elements is usually gray or white – stones, for example.

Follow up: Why is dust usually grey?

Aluminum oxide. The most common metal in the Earth’s rust is Aluminum, the most common element in the Earth’s crust is oxygen. Put them together and you get Aluminum oxide. There’s also a lot of silicon, meaning silicon dioxide (glass) is also very common (silicon is the second most common element in the crust, aluminum being 3rd) but it doesn’t have much color of its own, so the aluminum takes over.

Places with red sands generally have more iron, getting a red color from iron oxide (ie Mars) and black sands are created from volcanic activity, creating basalt which is black due to minerals like augite.

Also, are you thinking of dirt or soil? A lot of the stuff that plants grow in is brown because it’s full of organic matter not just rocks and minerals. And it’s very location dependent, I am in Australia where a lot of the dirt is red, not just in the outback but where crops are grown too. It’s amazing to see a freshly tilled field of all red furrows!

Hilariously both of these answers are wrong, it’s a combination of iron oxide which has a distinct red color (it’s what covers the Martian surface), and also organic material which gives it that darker brown color, also why potting soil is more black than your normal dirt (at least in regions that don’t have “good” soil)