Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.
Why don’t rocks burn? – Luke, age 4, New Market, New Hampshire
While many rocks don’t burn, some of them do. It depends on what the rocks are made of – and that’s related to how they were formed.
There are three main rock types: igneous, sedimentary and metamorphic. These rocks are made of minerals that all have different characteristics. Some will melt into magma or lava – super-hot, liquid rock – when they are exposed to heat. Others will catch fire.
Rocks that burn when they get heated up are combusting. This means that elements within the rocks are reacting with oxygen in the air to produce heat and light, in the form of flames.
The elements sulfur, carbon and hydrogen easily react with oxygen. Rocks that contain these elements are combustible. Without these elements inside them, rocks that are exposed to enough heat will melt instead of catching fire.
How rocks form
Igneous rocks are formed when magma underground or lava from a volcano cools and crystallizes into solid material. These rocks are mostly made of silicate minerals that crystallize at temperatures from 1,300 degrees Fahrenheit (700 degrees Celsius) up to as high as 2,400 F (1,300 C).
Igneous rocks contain few or no combustible elements. And it’s very hard to remelt them back into magma because they crystallize at such high temperatures – it would take the kind of high-tech incinerator that cities use to burn waste to make that happen.
Sedimentary rocks have a very different formation story. They form from broken bits of rocks, minerals, sometimes plant or animal material, and also crystals left behind when water evaporates, like the limescale that forms in teakettles and bathtubs.
There is a lot of sulfur, carbon and hydrogen in living things. In fact, these are three of the six essential elements of life on Earth. Bits of organic matter, particularly dead plants, also are combustible and allow the rocks to burn.
The last group of rocks is called metamorphic, because these rocks form when a lot of heat and pressure change existing rocks into new types without melting or burning them. “Metamorphosis” comes from ancient Greek and means “transformation.” For example, marble that you might see in kitchen counters or statues came from limestone that was transformed under intense heat and pressure deep underground.
The rock that humans burn: Coal
Metamorphic rocks that are formed from igneous rocks won’t contain the combustible elements – the ones that burn – but metamorphic rocks made from sedimentary rocks might. One familiar example is anthracite coal, which is made almost entirely of carbon. It formed when dead plants fell into swamps long, long ago, were buried by sand or mud, and eventually were compressed over hundreds of millions of years into coal.
There are many coal seams around the world. Sometimes the coal even catches fire while it’s still in the ground. The cause can be natural, such as a lightning strike, or human activities like mining.
If carbon is compressed with even more pressure than it takes to make coal, eventually you get diamonds – the hardest mineral found in nature. In 1772, French chemist Antoine Lavoisier proved that diamonds could combust when he burned one with a magnifying glass.
Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.
And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.
The elements sulfur, carbon and hydrogen easily react with oxygen. Rocks that contain these elements are combustible. Without these elements inside them, rocks that are exposed to enough heat will melt instead of catching fire.
Igneous rocks contain few or no combustible elements. And it's very hard to remelt them back into magma because they crystallize at such high temperatures – it would take the kind of high-tech incinerator that cities use to burn waste to make that happen.
When heated, this water expands rapidly, exerting pressure from within.This can cause rocks, particularly porous varieties, to shatter violently in a camp fire, sending fine, sharp pieces of rock shrapnel flying into the air.
It takes temperatures between 600 and 1,300 degrees Celsius (1,100 and 2,400 degrees Fahrenheit) to melt a rock, turning it into a substance called magma (molten rock).
The elements sulfur, carbon and hydrogen easily react with oxygen. Rocks that contain these elements are combustible. Without these elements inside them, rocks that are exposed to enough heat will melt instead of catching fire.
Explanation: Stones are bad conductors of heat. Most of the stones tend to disintegrate when cooling after being heated by fire. Granites disintegrate under fire.
Also, Rock (and Ground) being super effective against fire is because one of the most effective methods of putting out a fire is to smother it. Dropping a pile of dirt or a large enough rock directly onto a fire will cut off its oxygen supply, causing the fire to go out.
Fires were set against a rock face to heat the stone, which was then doused with liquid, causing the stone to fracture by thermal shock. Rapid heating causes thermal shock by itself—without subsequent cooling—by producing different degrees of expansion in different parts of the rock (and in other materials).
Rocks. Not all rocks are suitable for use in a fire pit, so make sure you check the type of stone before using it. Porous or wet stone, such as sandstone or river rocks, may crack or explode when they reach high temperatures. Hard rocks like granite, marble or slate are suitable for use in fire pits.
Flint rocks, such as quartz, agate, chert, and jasper, which are high in silica content, are needed for striking fires. These stones have a smooth, glassy appearance.
Fire proof- rock is not a flammable material and can be a good option for areas near a fire pit. Durability- rock isn't going to be affected by the elements and it will withstand more wear and tear than mulch.
Placing firewood in a ring of rocks can be a good way to lessen the risk of starting a wildfire, as well as acting as a barrier for wind that might blow out the early embers, but you need to be very choosy with your selection. Crucially, don't ever use river rocks.
If there is too much heat or pressure, the rock will melt and become magma. This will result in the formation of an igneous rock, not a metamorphic rock.
Common choices include basalt, gabbro, granite, and volcanic rocks like peridotite. These stones are prized for their durability, ability to retain heat, and resistance to thermal shock.
Since the thermal conductivity for stone is high, the heat will move quickly through the stone and away from you, similar to how running water flows through a funnel faster than it would through a sponge. The sense of coolness that you feel happens because the heat is flowing out of your body and through the stone.
This happens because of a process known as pyrolysis, which causes the organic (carbon-based) compounds that makes up the wood to decompose into gases like methane and some more complex hydrocarbons. These in turn burn as they combine with the oxygen.
A purely stone structure indeed cannot be consumed by fire (except by a nuclear explosion or a volcano). However, there are precious few purely stone structures, especially ancient ones.
Stone. Stone suffers under the effects of fire and is prone to disintegration when suddenly cooled. Based on the specific type of stone, the exothermic reactions can vary greatly. For example, granite explodes when exposed to heat – and therefore requires extensive risk management when used as a construction material.
Stone piece is composed by small pieces of rocks and clay. So it does not have organic matter in it to burn in presence of air. Hence, it is a non combustible.
Address: 743 Stoltenberg Center, Genovevaville, NJ 59925-3119
Phone: +2202978377583
Job: Administration Engineer
Hobby: Surfing, Sailing, Listening to music, Web surfing, Kitesurfing, Geocaching, Backpacking
Introduction: My name is Rubie Ullrich, I am a enthusiastic, perfect, tender, vivacious, talented, famous, delightful person who loves writing and wants to share my knowledge and understanding with you.
We notice you're using an ad blocker
Without advertising income, we can't keep making this site awesome for you.
