Why Rocks Don’t Burn: The Science Behind Incombustible Rock

Oleh: Natalie Bursztyn

LOTS incombustible rock. However, there are also those that can be engulfed in flames.

It all depends on what the rock is made of. This is related to how the rock was formed.

Also read: Can Stones Get Bigger?

There are three main types of rock: Igneous rock, sedimentary rock, and metamorphic rock. These rocks are made of minerals that have different characteristics.

Some of them will melt into magma or lava – very hot molten rock – when exposed to heat. Others will burn.

When heated, burning rock will experience combustion. That is, elements in the rock react with oxygen in the air to produce heat and light in the form of fire.

Elements such as carbon and hydrogen sulfur readily react with oxygen. Rocks containing these elements are flammable. Without these elements in them, rocks exposed to heat at certain temperatures will melt, not burn.

How are rocks formed?

Igneous rock forms when underground magma or lava from volcanoes cools and crystallizes into solid material. Most igneous rocks are made of silicate minerals that crystallize at temperatures of 700 degrees Celsius to 1300 degrees Celsius.

Igneous rocks contain little or no combustible elements.

It is very difficult to melt igneous rocks back into magma because they crystallize at very high temperatures.

We need the high-tech incinerators cities use to burn trash to make this happen.

Also read: How is Coal Formed?

Sedimentary rocks have very different formation stories. Sedimentary rock is formed from fragments of rock, minerals, sometimes plants or animals.

There are also crystals left behind when the water evaporates, such as scale like those that form on teapots and bathtubs.

There is a lot of sulfur, carbon and hydrogen content in living things. In fact, they are part of the six essential elements of life on Earth.

Scraps of organic matter, especially dead plants, are also flammable allowing rocks to smolder.

The last group of rocks is called metamorphic. These metamorphic rocks form when a great deal of heat and pressure converts existing rock into a new type without melting or burning it.

“Metamorphosis” comes from ancient Greek and means “change”.

For example, the marble you might see on kitchen countertops or statues comes from limestone that changes under intense heat and pressure underground.

Coal, stone burned by humans

Metamorphic rocks that form from igneous rocks will not contain any combustible elements.

However, metamorphic rocks that form from sedimentary rocks can contain combustible elements.

One common example is anthracite coal: it is composed almost entirely of carbon.

Also read: Hundreds of Rare Crystal Stones Found in Prehistoric Cemeteries, What For?

This coal was formed when dead plants fell into marshes in the past, were buried by sand or silt, and finally compressed over hundreds of millions of years.

There are many layers of coal scattered beneath the surface of the earth in all corners of the Earth. Sometimes coal even burns while still in the ground.

The causes can be natural, such as lightning strikes, or due to human activities such as mining.

In Centralia, a former mining town in Pennsylvania, coal seams have been burning for more than 50 years.

There are also other active coal seam fires in places around the world including Zimbabwe in Africa and Jharia in India.

Carbon pressed with even more force can form into diamonds – the hardest mineral on Earth. In 1772, the French chemist Antoine Lavoisier proved that diamonds could burn when he set them on fire with a magnifying glass.

With enough patience, you can burn diamonds in a candle flame. However, diamonds are quite expensive.

You’re better off trying to burn something else made of carbon, like leaves, under a magnifying glass, or twigs and marshmallows in a campfire.

Also read: What is the Hardest Rock in the World?

Natalie Amber
Lecturer in Geosciences, University of Montana

This article was published on Kompas.com in collaboration with The Conversation Indonesia. The text above is taken from the original article entitled “Why can’t rocks burn?“. The contents are beyond the responsibility of Kompas.com.

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2023-06-29 13:34:00
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