Shulou(Shulou.com)11/24 Report--

The original title: "there is an island floating on the sea, and it is a pile of stones floating on the water." "

It is common sense that a stone sinks as soon as it enters the water, but the stone I am going to introduce below is not a "regular stone".

Pumice | Source: Wikipedia it is called pumice (pumice), the name has already pointed out what makes it different.

Photo Source: when gfycat sees the pumice, you can immediately understand why it floats on the water. It looks like a petrified SpongeBob.

The holes in pumice account for 64% to 85% of the total volume, which means that it is filled with air, and only a small part of the minerals are composed of silica.

A roll of banknotes can support pumice | Image Source: how is SpongeBob in the Wikipedia stone world formed?

Because it often appeared on the sea or by the sea, the ancients thought it was consolidated by floating foam on the sea. But its birth mother is not tender water, but a grumpy volcano.

Image source: after the Wikimedia Commons volcano erupted, a large amount of hot magma poured into the cold sea water, which cooled rapidly, the internal pressure dropped sharply, and the gas solubility decreased. Just as the newly opened Coke bottle releases a lot of carbon dioxide, the gas originally dissolved in the magma escapes to form bubbles. As the magma solidifies in an instant, gases such as carbon dioxide bubbles and are frozen in it, forming a large number of holes. So pumice is also a kind of volcanic glass.

Some of these volcanoes come from the shore, and some are hidden at the bottom of the sea. Generally speaking, the pumice produced by volcanic eruptions on shore is relatively small and no bigger than golf balls. Undersea volcanoes spray magma directly into the sea, producing pumice about the size of an apple. They are distributed within thousands of meters of the volcano. A large number of pumice stones are sometimes gathered together to form a floating island, called a pumice raft (pumice raft).

Pumice raft near Tonga Islands was captured by satellite. Source: NASA2019 year, a 150 square kilometer "floating island" appeared in the tropical waters near Tonga Islands, which was formed by undersea volcanic eruptions.

A large number of pumice on the pumice raft | Source: ayman masry pumice raft is covered with large and small, dense pumice, smelling of sulfur, moving all the way to Australia. Scientists believe it will bring new life to the declining Great Barrier Reef.

Pumice will travel long distances at sea. In 1979, huge pumice rafts formed by undersea volcanic eruptions near Tonga drifted hundreds of kilometers away to Fiji. Pumice formed by the eruption of Krakatoa has been floating in the Indian Ocean for 20 years. These floating stones sometimes threaten passing ships.

However, pumice will not wander forever, and they will eventually sink to the bottom of the sea or be sent ashore.

Image source: Wikimedia Commons this is because the stomatal structure of pumice is not completely sealed, but partially connected with the outside world. With the gradual depletion of gas and the invasion of water, pumice will eventually end its floating life.

But what puzzles scientists is that even if a sponge is completely soaked, it will sink, and the sea is rough, why can pumice float for years?

Scientists at Berkeley Lab used synchrotron X-rays to scan pumice and build 3D models to see through the mystery.

Large bubbles (top) and all bubbles (bottom) in 3 pumice samples | Source: Fauria, K. E., Manga, M., & Wei, Z. (2017) they found that there was a game with water behind the rise and fall of pumice. Pumice is covered with many tiny pores with wide hair diameters, and the surrounding water infiltrates along the pores under the action of capillaries, and surrounds the gas in which there is no escape, forming bubbles. Because of the surface tension of the water, these bubbles are difficult to move and are trapped in the stone.

Water (blue) enters the pumice hole and surrounds the gas (white) to form bubbles | Source: Fauria, K. E., Manga, M., & Wei, Z. (2017) however, with the liquid seepage, these gases will gradually spread out and eventually sink into the sea. The scientists used the percolation theory (percolation theory) to describe the process to predict how long the pumice would float.

The researchers also found an interesting phenomenon in the laboratory: some pumice floats during the day and sinks at night.

Is this guy going to sleep?

These stones are not because they are tired of floating and want to rest at night, but because they are "cold". When the temperature is high during the day, the bubbles in the pumice expand, resulting in greater buoyancy; in turn, at night, the temperature decreases, the bubbles become smaller, the water seeps in, and some pumice cannot hold up.

After heating, the pumice (the rightmost 2) bubbles (white) decreased, while the water permeability (blue) increased. Source: Fauria, K. E., Manga, M., & Wei, Z. (2017) after the researchers directly heated the pumice with high temperature, the pumice could not float at all. X-ray scan results show that the bubbles are much smaller and are occupied by the current.

Pumice not only has special physical properties, but also contains the history of geological and biological evolution. Pumice from underwater volcanoes brings to the surface the secret of sleeping at the bottom of the sea. The porous structure of pumice enriches a lot of nutrients, creating living conditions for algae, coral polyps and other animals and plants. These creatures wander with pumice and are taken to all parts of the world to take root in their new homes.

In addition to the research value, pumice is also used in all fields of human life.

The porous nature of pumice is suitable for grinding things. The most common is rubbing stone, which is used to grind off the thick stratum corneum on the soles of the feet.

Pumice can also be used as a skin exfoliator after grinding into powder. Thousands of years ago, the ancients did not have as many toiletries as they do now, and they used pumice to remove hair, calluses, and sharpen their nails. The ancient Romans would also add pumice powder to toothpaste as a polishing agent to wear off dental plaque, but it can also hurt teeth if it is overworn.

Pumice is a bit ruthless on people, but it is good as a powerful cleaner and can easily wear off scale and rust. The clothing industry also uses pumice to wash jeans to create a popular old-fashioned feeling.

The light pumice is not suitable to be used as a building material directly, but after grinding it can be added to the concrete as a cementitious material to improve the durability of the concrete.

In horticulture, pumice is used to decorate bonsai. Mixing it with the soil can also enhance the drainage and air permeability of the soil and make the plants grow better.

Seemingly "frivolous" and unhandsome pumice, this is not much more than how many "vase" stones?

This article is from the official Wechat account: take Science Home (ID:steamforkids), Mirror

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