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Rocks can explode when heated. This statement should be convincing enough not to boil rocks, place them into the oven or inside the fireplace. That is why we are speaking about this topic today. We want to figure out what physical properties of the rocks are in charge of the explosion. What types of rock are prone to explode, and what types are relatively safe.
Rocks that are composed of different minerals are more likely to explode than any monomineralic ones because of the different physical properties of composing minerals. Also, the porous rocks or the layered rocks are possibly dangerous when heated, as they can have water inside.
An explosion is a bit too exaggerated for the process which takes place inside a piece of rock. There are no fiery sparks during rock explosions. Rocks explosion is the debris of rocks that are accelerated by rapid pressure discharge. However, these flying rocks are also very dangerous. Today we will teach you how to tell if the rock is potentially explosive or not when heated.
If you are interested in checking out the best books about rocks and minerals identification you can find them by clicking here (Amazon link).
Do Rocks Explode When Heated
Rocks explosion is an unpredictable phenomenon. Some people can live a whole life and not experience any rock explosion. But sometimes rock explosions can cause a lot of problems.
Rock debris can hit a human or damage some home facilities, cars, clothes, etc. That is why we recommend people to be careful with rock heating. Further, we will discuss why rocks explode, what types of rocks are more prone to explosion, and many other facts.
Rocks explode when heated. Porous, layered, and multi-mineral rocks like shales, slates, mudstones, schists, and limestones are prone to explosion because of different mineral compositions and water trapped in the pores. Due to rapid heating, the rocks can crack and explode into dozens of debris.
Nearly any type of rock has the potential to explode. There are two main reasons why rocks explode when heated, no matter do they have sedimentary or magmatic origin:
- Porous and wet rocks are likely to explode when the rock is heated up. The trapped air and water expand very quickly and forcefully break the rock apart, sometimes causing it to explode.
- The rock composed of different minerals is also prone to explosion. Rocks are usually made up of different minerals with different physical properties (density, thermal conductivity, thermal expansion, stress-strain relationship, elastic constants, and so on). Because the different types of rock expand differently when exposed to heat, the rock expands asymmetrically, which can cause a violent shattering of the rock when exposed to high heat.
We can make the next conclusion from the above. The porous, polymineralic, and wet rock of any origin is more likely to explode.
Can Rocks Explode if Boiled?
Some porous and layered rocks can explode when boiled. Especially if the heating was too rapid or the rock had been placed into boiling water. An instant temperature change creates a rapid change of pressure inside the rock. The pressure can be released by the rock explosion.
Will Rocks Explode in the Oven?
Not every rock will explode in the oven; however, you should keep it in mind and not place a layered, highly porous, or wet rock inside the oven. The oven temperature is higher than that of boiling water, so there is a higher probability of rock explosion.
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Why Do Some Rocks Explode in Fire
The most common situation when rocks explode is when they are placed around the fireplace. In that case, the rock is subjected to rapid and unidirectional uneven heating. One side of the rock remains cool, while the other is extremely heated.
There are two main reasons for the rocks’ explosion. The first one is the presence of water in pores or cracks in the rock. Water acts as a hydraulic press inside the rock when heated. The second reason is different minerals with strikingly different physical properties, make up the rock.
All types of rock can explode in a fire; however, there is a striking difference in probability between sedimentary, metamorphic, and igneous types of rock.
Sedimentary rocks (limestone, sandstone, shale, breccia, and conglomerate) are more likely to trap the water and, as a result, to explode in fire. All of them are not compacted enough and have a lot of pores, where the water can be absorbed.
Intrusive igneous rocks (granite, gabbro, anorthosite, syenite) are generally not so prone to explode because of two factors: they have already experienced high temperatures during the formation, and they are solid and have no pores to trap the water.
However, some volcanic (extrusive) igneous rocks (basalt, pumice, rhyolite, andesite, dacite) can be porous and soak some water. Please, be careful with volcanic rocks.
Metamorphic rocks can be also divided into two groups that will not explode and that probably can.
- Foliated metamorphic rocks like slate are really hard rocks; however, because of foliation, the water can be trapped between layers and can lead to an explosion.
- Non-foliated metamorphic rocks (hornfels, skarn, quartzite, and marble) won’t explode when heated. These rocks had already experienced high temperature and pressure and had no pores. Very extreme heat, unattainable under common fire conditions, should be applied to them to produce an explosion.
Also, a general rule with water should be remembered!
Wet rocks are much more likely to explode than dry rocks. Make sure you never select rocks near or out of water. Even if they are the right type of rock, they will probably blow up from the trapped water inside.
TIP: Do you know what determines rock colors? There are different factors that determine rock colors. Find them out in the article below:
Rock Colors: What Determines Color & Why Different Colors
What Kind of Rocks Explode in Fire
Porous, less compacted, polymineralic rocks are more likely to explode in fire. All these factors are usually common to sedimentary rocks, foliated metamorphic rocks, and porous volcanic igneous rocks.
Sedimentary rocks are mostly prone to explode in fire because of their porosity and cavities in the structure. Water can be trapped in these natural holes and contribute to the explosion of the rock. Limestones, shales, and conglomerates are the most dangerous rocks to put on a fire.
Except for sedimentary rocks, foliated metamorphic rocks and volcanic (extrusive) igneous rocks can also explode.
These types of rocks are prone to explosion because of the presence of pores and layers. Water can penetrate igneous and metamorphic rocks and make them pop up when heated.
Do Lava Rocks Explode?
Lava rocks (basalt, pumice, rhyolite, andesite, dacite) are less likely to explode as they have already experienced heating during the formation. However, because of lava rock porosity, water can be trapped inside. In case wet lava rock is heated, it can end up with an explosion.
Do River Rocks Explode in Fire?
River rocks can be composed of any type of rock (sedimentary, igneous, and metamorphic). It’s hard to tell if it explodes or not based on composition only. However, if the rock has been taken out of the water or near the river, there is no doubt that it has water in its pores and can explode in fire.
Do Wet Rocks Explode in Fire?
Wet rocks are more prone to explode in the fire than dry analogs of the same mineral composition. Water seeps inside the rock and can stay in pores. Water expands and produces water vapor during heating. Vapor tries to escape and find its way out by expanding the rock. We observe it as an explosion.
TIP: Rivers are a great place for rockhounding. Do you know what common rocks you can find there? Check them out in the article below:
Ten Most Common Type of Rocks You Can Find In Rivers
How Hot Do Rocks Have to Get to Explode (What Temperature)
History knows when the rock explodes being boiled. That means that such a low temperature like 100°C can be enough to blow up the rock.
Sometimes people place rocks into boiling water or into the oven to disinfect the rock. But it is extremely dangerous as the rock can pop up and explode.
Rocks can explode even in boiling water (100°C) and an oven (up to 250°C). Average fire flame temperature ranges from 525°C to 1000°C. Orange flames reach 1200°C. In the white part of the flame, the temperature can reach up to 1300°C. The hotter the flame, the higher the probability of the rock’s explosion.
Igneous rocks have already experienced high temperatures during their formation. The temperature of igneous rocks magma reaches up to 1200°C. Granite solidifies at 650-700°C. Igneous rocks are far more resistant to high temperatures.
Metamorphic rocks are also formed as a result of a high-temperature combination with high pressure. The temperature of some metamorphic rock formations reaches 700-900°C.
Non-foliated metamorphic rocks like quartzite, marble, and gneiss are strong enough to withstand the temperature of the fire and do not explode.
Sedimentary rocks didn’t experience any elevated temperature and pressure during their formation, so even small temperature fluctuations can cause the explosion of sedimentary rocks.
Also, sedimentary rocks are highly porous because of the slight compaction of mineral grains. Pores, cavities, and cracks can trap water and oil inside. Rapid heating of sedimentary rock will create an inner pressure that can end up with an explosion.
TIP: Do you know how long does it take to form a rock? It takes a different time for different types of rocks. Find out the exact values for all types of rocks in the article below:
How Long Do Rocks Form? Answers For ALL Types of Rocks
11 Rocks that Explode When Heated
Almost all sedimentary rocks, volcanic igneous rocks, and foliated metamorphic rocks can explode when heated.
The water, trapped within inaccessible pores within the rock, heats up and thus builds up tremendous energy, causing the rocks to crack and even to explode violently with dozens of debris. Further, you will see the list of the most common explosive rocks.
Porous and layered sedimentary rocks like limestone, sandstone, shale, and conglomerate, and breccia can explode when heated. Extrusive igneous rocks (pumice, basalt, rhyolite, andesite, dacite) and foliated metamorphic rocks (slate) can explode if they contain water inside. River rocks can also explode.
Here is the list of the most common sedimentary rocks people usually run into when they want to make a campfire.
Limestone, slate, pumice, breccia, conglomerate, and river rocks are rocks that can be potentially explosive, especially if they contain water in pores, cavities, and cracks.
Limestone is a highly porous sedimentary rock that can explode when heated. Limestone has numerous cavities that can be potentially filled with water.
During rapid heat, water vapor will be created. The vapor expands the pore and as a result, produces a crack and pushes debris in different directions.
Slate is a foliated metamorphic rock. Its physical property varies dramatically depending on the direction because of the rock’s foliation.
Slate is very strong and resistant, however, can be easily destroyed if the force is applied along foliation. That is why it can explode and contain water between layers.
River rocks are any kind of rocks found near or in the river. They are usually smooth and tumble. River rocks can explode because they contain water in pores and cavities.
Even if you see a river rock of igneous or metamorphic origin, please don’t put it near the fire.
Even though pumice is extrusive igneous rock it is highly porous and potentially explosive. Pumice is so porous that it is considered the lightest rock.
Because of pores, pumice can float on the water. Water can be soaked by pumice. Highly saturated pumice can explode in a campfire.
TIP: River rocks are usually smooth and tumble. Do you know how to tumble rocks at home without using a rock tumbler? Check out the ultimate guide in the article below:
Can You Tumble Rocks Without a Tumbler? Step-by-Step Guide
10 Rocks that Won’t Explode When Heated
All types of rocks have the potential to explode, however, the next 10 rocks are the strongest and need a really high temperature (almost inaccessible in a campfire) to explode. They are already tempered during the formation, so these 10 rocks are the best to use around a campfire.
Intrusive igneous rocks like granite, anorthosite, syenite, gabbro, diorite, and non-foliated metamorphic rocks like gneiss, hornfels, skarn, quartzite, and marble won’t explode when heated. These rocks had already experienced high temperature and pressure and had no pores to trap the water.
Quartzite, gneiss, and marble are the most common non-foliated metamorphic rocks. Quartzite, marble, and gabbro are monomineralic, which means they are composed of one type of mineral (quartz in the case of quartzite and calcite in the case of marble).
Additionally, quartzite and marble are not porous, so the water cannot penetrate the rock structure.
Quartzite is a really hard-to-destroy rock. It is monomineralic – each grain has the same physical properties. It is made of quartz – a really hard mineral (7 on the Mohs scale). It is a non-foliated metamorphic rock, which has already experienced high pressure and high temperature during formation.
Gneiss is a metamorphic rock. It won’t explode when heated as mineral grains are tightly interlocked with each other and have no pores and cracks to contain water.
Gneiss is formed due to extreme pressure and temperature conditions, so the fire heat is not enough to produce an explosion.
Marble is a non-foliated metamorphic rock composed of carbonate minerals: calcite or dolomite.
Crystals are closely interlocked and are strong enough to withstand rapid heating. The marble won’t explode when heated. Due to marble durability and heat resistance, it is widely used in fireplace facing.
Gabbro is a coarse-grained, dark-colored, intrusive igneous rock. It is mainly composed of plagioclase and pyroxenes.
It formed as a result of magma solidification, so minerals are crystallized closely with each other. It has no pores to trap the water and won’t explode when heated.
BTW: Do you want to know more about rock and mineral identification? The books listed below are the best ones you can find on the internet (Amazon links):
- Smithsonian Handbooks: Rocks & Minerals
- Gemstone & Crystal Properties (Quick Study Home)
- Ultimate Explorer Field Guide: Rocks and Minerals (National Geographic Kids)
Every rock may explode, so you should be very careful when placing it into the fire, especially in the oven or boiling water at home. However, some rocks are more likely to explode than others. There are two main causes of rocks’ explosion:
- The presence of water in the pores, cracks, and cavities.
- Strikingly different mineral composition of the rock.
Water is mostly present in sedimentary porous rocks like limestone, sandstone, shale, conglomerate, and breccia and they are more prone to explosion when heated.
Such rocks as slate and other foliated metamorphic rocks are also likely to explode when heated as they can contain water between layers.
Volcanic (extrusive) igneous rocks like pumice, basalt, rhyolite, andesite, and dacite are porous and can also explode if they contain water.
The hardly explosive rocks belong to non-foliated metamorphic rocks (gneiss, quartzite, marble, hornfels, skarn) and intrusive igneous rocks (granite, gabbro, diorite, syenite, anorthosite).
These rocks have no pores and do not soak water. Also, these rocks have been already exposed to high-pressure / high-temperature conditions, which makes them resistant to temperature fluctuations.
Even if you can clearly distinguish the type of rock, and you are sure that it will not explode, please, avoid placing the rocks under the fire.
It’s better to place rocks around the fireplace avoiding contact with coal or wood. Anyway, avoid river rocks or any wet rocks after the rain of any origin.
TIP: Have you ever heard of sailing rocks? The rocks move without any help. Find out the explanation of this natural phenomenon in the article below:
Sailing Stones Explained: Why & How Do They Move? (7 Facts)