Is ice a rock? It may seem a difficult question. Ice is clearly dissimilar to most of the rocks you can imagine. But to answer this question, you first need to analyze the definition of rock.
Before answering the question – is ice a rock – let’s first investigate if ice could be called a mineral.
Is ice a mineral?
Let’s start with the basic definition of a mineral. According to International Mineralogical Association, there are four criteria for a substance to be a mineral.
- Firstly, it must be a naturally occurring substance formed by natural geological processes. Obviously, ice forms naturally from water.
- Also, the material must be a solid substance in its natural occurrence. Again, ice is solid. Water is liquid, so it cannot be called a mineral, even when its chemical basis is the same.
- The third criterion requires that the substance would have a well-defined crystalline structure. Ice has a clear structure. In ice crystals, water molecules are arranged in layers of hexagonal rings. Again, pure water does not have a crystalline structure.
- The fourth criterion states that the substance must have a well-defined chemical composition. Of course, ice is always H2O. So, ice meets all the criteria to be a mineral.
Are there any exceptions when ice is not a rock?
Yes, there are two exceptions.
According to the first earlier provided criterion, minerals have to be formed naturally. So ice is not a mineral if it is human-made. In this case, it does not satisfy the first condition, even when otherwise it is identical to the matter that forms glaciers or icicles.
Of course, it is just a game of words – from the purely physical perspective, ice is nothing else but ice, contains the same frozen water, and has the same crystal lattice.
The second exception is related to the fourth criterion. Rocks must have clearly defined chemical composition. They also need to be inorganic. If there is any organic material in ice, these conditions are not met. So, for example, if you find a frozen insect, it is not a rock – even when it is large and it is frozen rock-solid.
If ice is a mineral, is it a rock then?
Now, when we are sure that ice is a mineral, we can go further and answer if water is a rock, because these two concepts are distinct from each other.
In fact, according to the official definition, rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter.
So, ice can be considered rock, at least if you take into account a sufficient amount of it and pack it into a single mass to make it more or less solid. One snowflake is a mineral too, but it would be too little to be considered an aggregate of minerals. But a tightly compressed snowball is clearly a rock. Remember that when you throw snowballs at your friends, you are actually throwing real rocks!
What type of rock is ice?
Can there be different kinds of water-based ice? Yes, there can be. According to geologists, we can classify rocks according to the mechanisms that led to their formation. There are two distinct ways for ice to form:
1. When a rock forms through the action of pressure and (or) heat, it is called metamorphic. In our case heat is not applicable, but pressure is. When a large amount of snow accumulates in a single place, it gets compressed by its own weight until individual snowflakes get transformed into large ice crystals. This way, an entire glacier can be considered a single large rock.
2. If a rock forms due to processes of sedimentation, it is called sedimentary. You probably did not know, but all snowflakes form through so-called chemical sedimentation – they precipitate out of the air when the air is oversaturated with water. Then, snowflakes fall to the ground and often form granules of ice, when the ambient conditions are just right, or when they stay on top of each other for a longer time. Such partially compacted snow – called firn – can be considered a sedimentary rock.
It may seem strange to call ice a mineral or a rock. But if we classify all things according to certain rules, we must admit that ice is not an exception. While a single snowflake is too soft and too small, lots of snowflakes compacted into a single snowball become a full-fledged rock.