What's the secret behind the bright colors lighting up the US night skies on the 4th of July?

The answer is minerals! Each color is the result of specific chemicals derived from different minerals. Read further to find out what these minerals are, and get ready to be surprised at the other ways these minerals are used when they're not competing with the stars to illuminate the night sky.

The Color: Green

The Chemical: Barium Chloride

Mineralogy 101: Barium chloride is what's known as a metal salt. Barium, though, comes from minerals, most commonly from barite.

Its Other Uses: Most people's personal experience with barium is likely tied to the doctor's office. Because barium is not absorbed by the body but is very good at blocking radiation, people suffering from a variety of digestive issues are often given a barium 'milkshake' prior to having x-rays or scans of the esophagus, stomach or small intestine. When these organs are coated with barium, they stand out more clearly on the scan, allowing easier detection of irregularities. Barium's ability to absorb radiation is why barite is commonly used in the concrete of radiation shielding in hospitals, laboratories, and nuclear facilities.

Medical applications, however, represent a very small percentage of barite used in the United States. The United States is the world's leading barite consumer, with more than 90% of the barite sold domestically used in drilling fluids. The name barite is derived from the Greek word for heavy. Because of its high density, barite is used as a weighting agent in fluids (also known as muds) used for drilling oil and natural gas wells. The weight of the drilling mud suppresses high pressure from the oil and gas and helps prevent blowouts.

Where Does It Come From: Only one barite mining facility remained open in 2020 in the United States, located in Nevada. The other mining and processing facilities in the United States were idled. China is the global leader in barite production.

The Color: Blue

The Chemical: Copper chloride

Mineralogy 101: Like barium chloride, copper chloride is a metal salt. There are several natural but relatively rare mineral forms of it – eriochalcite, nantokite, and tolbachite.

Its Other Uses: Copper was one of the first metals used by humans and has played an important role in the development of civilization. The vast majority of copper today is used for electrical purposes, such as power generation and transmission.

Where Does It Come From: The largest reserves of copper in the world are found in Chile, which is also the single largest producer of copper. In 2020, U.S. mine production of copper decreased by an estimated 5%, while global production of copper also declined slightly to an estimated 20 million tons in 2020 from 20.4 million tons in 2019, owing primarily to COVID-19 lockdowns in April and May.

The Color: Yellow

The Chemical: Sodium Nitrate

Mineralogy 101: Another salt, sodium nitrate's mineral form is known as nitratine.

Its Other Uses: Although salts are a general class of chemicals, sodium is the metal most commonly associated with salts. Sodium forms many different salts, each of which has various uses.

The most common and abundant sodium salt is sodium chloride. Although well known as table salt, sodium chloride's major uses include highway deicing, chemical feedstock and food processing.

Sodium nitrate is a type of saltpeter, which is most well-known for its use in the production of gunpowder.

Sodium sulfate is another common sodium salt, which has many uses. It is used in glass-making to remove air bubbles, in textiles to allow for even absorption of dyes, as filler in detergents, and in processing wood pulp for paper production.

A fairly new use for salts such as sodium sulfate and sodium nitrate is in thermal energy storage, because these salts can absorb heat and slowly release it.

Where Does It Come From: The global COVID-19 pandemic affected production and consumption of salt throughout the world in 2020. The most significant impact was felt in the chloralkali industry because international trade declined, but the entire salt sector was negatively affected to varying degrees. The chloralkali industry was also disrupted by severe weather events, mainly hurricanes, in the primary production areas of Louisiana and Texas.

The Color: Red

The Chemical: Strontium nitrate

Mineralogy 101: Strontium is element number 38 on the periodic table and commonly occurs in nature, but seldom in quantities sufficient for economic recovery. The strontium nitrate used in fireworks is actually a strontium salt, and the source of the strontium is usually the mineral celestite.

Its Other Uses: Strontium compounds can be used in ceramic ferrite magnets (like refrigerator magnets and for small motors), master alloys to make aluminum castings, in the electrolytic production of zinc, and as an additive in glass. Since 2006, it is thought that virtually all the strontium minerals consumed in the United States were used in drilling fluids for oil and gas wells, similar to the way barite is used.

Where Does It Come From: Although deposits of strontium minerals occur widely throughout the United States, none have been mined in the United States since 1959. The United States relies 100% on imports for strontium minerals.

The Color: Purple

The Chemical: Purple is made from a combination of strontium and copper, described above.

The vibrant colors that will fill the sky this Fourth of July are made possible because of the unique properties of specific minerals, just as minerals are essential to make so many other things that society relies on every other day of the year.

For more information on minerals, visit the USGS Minerals Resources Program website and follow the USGS Minerals Twitter account.

*This story was updated on July 2, 2021, from a previous story