Mercury sulfide

Some rocks are bright red.

They are made of two things. This red rock is found in nature. It is called cinnabar. It can be used to make paint.

There is also a black kind. The black kind is less common. You can turn the black kind into red. You do this with gentle heat. This red rock does not melt in water. It is a very pretty color.

Can you find something red today?

Mercury sulfide is a compound made of mercury and sulfur. It has the formula HgS. This substance does not dissolve in water. It can take two different shapes. The red shape is called cinnabar. This is how mercury is most often found in nature.

Cinnabar has a special crystal structure. It has coils of mercury and sulfur inside. These coils make the red crystals act in a special way with light.

There is also a black form called metacinnabar. This black form is less common. You can turn the black form into red. You do this by using gentle heat.

People can get mercury from cinnabar ore. They do this by heating it in the air. This makes a vapor. They then catch that vapor to get the metal. Some people use mercury sulfide to store mercury underground. This helps keep it safe from the air.

Mercury sulfide is a special chemical compound. It is made of two elements named mercury and sulfur. Scientists write its formula as HgS. This substance does not dissolve in water. It can exist in two different crystal forms. One form is red and is called cinnabar. This is the form most often found in nature.

Cinnabar has a very interesting way it works with light. Inside the red crystals, there are tiny coils. These are called Hg-S helices. These coils make the red crystals optically active. This means they interact with light in a special way. There is also a black form called metacinnabar. This black version is less common in the wild.

Making this compound can happen in a lab. Scientists can make black metacinnabar by treating mercury salts with H2S. They often use an acetic acid solution of mercury(II) acetate for this. You can change the black form into the red form. To do this, you must use gentle heating on the slurry. This process turns the black crystals into the red cinnabar form.

People use cinnabar to find real mercury. They take the cinnabar ore and roast it in the air. This creates a vapor. They then condense that vapor to get the metal. In the past, people used cinnabar as a red pigment. Some red walls in the old city of Pompeii turned dark. This happened because of mercury compounds and calcium sulfate.

Mercury sulfide is useful for keeping things safe today. Some industries use a process called the Castner–Kellner process. This process uses mercury cells. As these cells are phased out, the metal is turned into mercury sulfide. This allows for safe underground storage. It also has a band gap of 2.1 eV. This makes it possible to use in a photoelectrochemical cell.

Mercury sulfide is a chemical compound made of two elements. These elements are mercury and sulfur. Scientists use the chemical formula HgS to represent it. This substance is virtually insoluble in water. This means it does not dissolve easily when placed in liquid. It is a significant material because it exists in different crystal forms. These forms change how the substance looks and behaves.

This compound is dimorphic, which means it has two distinct crystal forms. The first form is red cinnabar, or alpha-HgS. This form belongs to the trigonal crystal system. It uses a rhombohedral crystal structure. Cinnabar is the version most commonly found in nature. The red color comes from its unique internal arrangement. Specifically, the structure contains Hg-S helices. These helices are tiny coils of mercury and sulfur. These coils make the red crystals optically active.

The second form is black metacinnabar, or beta-HgS. This version is less common in the natural world. It adopts a zinc blende crystal structure. You can create this black form in a laboratory setting. Scientists do this by treating mercury(II) salts with H2S. They often use an acetic acid solution of mercury(II) acetate. This reaction causes the black solid to precipitate. If you apply gentle heating to the resulting slurry, a change occurs. The black polymorph converts into the red cinnabar form.

Humans have used mercury sulfide for many different purposes throughout history. Cinnabar has long been used as a red pigment. In the past, people noticed that cinnabar tended to darken over time. For a long time, people thought this was because red alpha-HgS turned into black beta-HgS. However, researchers found a different reason at the excavations in Pompeii. The red walls in Pompeii darkened, but they did not contain beta-HgS. Instead, the darkening was caused by other chemical reactions. These reactions formed mercury-chlorine compounds like corderoite, calomel, and terlinguaite. They also formed calcium sulfate and gypsum.

Mercury sulfide is also a key step in producing pure mercury metal. To get the metal, people use cinnabar ore. The ore is roasted in the air. This process turns the solid into a vapor. The vapor is then condensed to collect the liquid mercury. This follows the chemical path of HgS turning into Hg and S. This method allows us to extract the element from its natural mineral form.

Today, mercury sulfide plays a role in environmental safety and modern technology. The chlor-alkali industry uses the Castner–Kellner process. This process involves the use of mercury cells. Because of concerns over mercury emissions, these cells are being phased out. To keep the environment safe, the metallic mercury is converted into mercury sulfide. This stable compound can then be used for underground storage. This prevents the mercury from escaping into the air or water.

There are also interesting scientific possibilities for this compound. Mercury sulfide has a band gap of 2.1 eV. This measurement describes how it interacts with energy. Because of this band gap and its stability, it can be used in a photoelectrochemical cell. This is a device that uses light to drive chemical reactions. Scientists have also looked at using sulfur to clean up mercury spills. They tried neutralizing the spills with sulfur. However, this reaction does not happen fast enough for emergency use. It is not yet a complete solution for rapid cleaning.