Beware: You should never explore wild caves alone or without proper gear. Consider getting in touch with a Grotto of the National Speleological Society at www.caves.org or a qualified cave club. These groups are skilled and will train you. Without sufficient knowledge, preparation, and equipment, cave exploring can lead to serious injury or death.
The world is full of wonders, and caves are one of them. Caves are dark, mysterious places with stalactites and stalagmites forming from the ceiling and floor. But in addition to cave formations, you may also encounter some vibrant minerals and crystals in the right kinds of caves. Notable locations include Naica Cave in Chihuahua, Mexico.
Some of these minerals retain value because of their appearance. People seek others out for practical applications in technology and manufacturing. This article will explore the minerals in these underground dens, so you can recognize some on your next trip.
Calcite
In terms of calcium carbonate polymorphs, calcite is the most stable one. Calcite is a common constituent of sedimentary rocks, forming when carbon dioxide releases from volcanic eruptions and precipitates as calcite.
As you can see from these examples, calcite is a source of calcium for plants to absorb. This leads us to believe that the caves were once submerged underwater, which caused certain minerals to form into different types of rock formations.
Oxide-hydroxides
Oxide-hydroxides are minerals that contain both oxides and hydroxides. They form both inside caves and out on the surface.
Many important products use oxide-hydroxides: cement, soil conditioners, or animal feed supplements.
The most common ones include white and black limestones, calcite, quartzite, and dolomite. The most common use of oxide-hydroxide is to increase soil fertility by adding calcium and magnesium, which helps plants grow better.
If you want to identify an oxide-hydroxide mineral, then look at its crystal structure first because there are many different types of interlocking patterns that could be present on this type of mineral, depending on which one it is.
Gypsum
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. Widely mined and used as a fertilizer, gypsum is the main constituent in the gypsum board.
Gypsum may be found anywhere that hydrogen sulfide gas (H2S) exists. This includes ocean floors and hot springs with high levels of dissolved sulfur dioxide (SO2).
The largest deposits are in New Mexico, USA; Usedom Island, Germany; Mexico; France; Canada; Poland; Iran; Saudi Arabia; China; India; Australia; Algeria; Kazakhstan (in combination with selenite); Russia (in a variety containing celestine), Germany (containing celestine), Jordan (containing celestine).
Sphalerite
Sphalerite, a mineral commonly found in caves and mines, is a magnificent crystal. It is a sulfide mineral, meaning it contains the elements zinc and iron, but also sulfur. Sphalerite can take many colors, but most commonly will be gray to grayish brown.
Halite (Rock Salt)
Sodium chloride is found in halite, a mineral found in caves all around the world. It has many uses, including as an additive to processed foods and animal feed. Halite even makes up artificial snowfall at ski resorts.
One of the most common substances on Earth, 47% of all known halite deposits exist within underground cave systems.
Halite is clear and colorless when pure, but impurities may give it a white or pinkish tinge. It has a Mohs hardness of 2 and is soft enough to be scratched by fingernails alone.
Halite is not radioactive; however, its presence could indicate radiation exposure from uranium decay products elsewhere in the environment.
Fluorite
Fluorite is a mineral with a hexagonal crystalline structure. The color of fluorite varies depending on its composition. You may find some in purple, green, or yellow.
People mine fluorite in its various forms all over the world. One more notable occurrence of unique fluorite crystals is at Treak Cliff Cavern near Derbyshire, England.
Fluorites from this location stand out due to their intense blue coloration – so much so that they earned the name “Blue John.” Treak Cliff is one of two sites where this fluorite is still mined today.
In addition to its use as an ornamental gemstone, fluorite is also used for industrial applications such as glassmaking and ceramics manufacturing. Its high index of refraction makes it ideal for lenses and prisms.
Aragonite
Aragonite is a carbonate mineral and the dominant form of calcium carbonate found in caves.
Stalactites and stalagmites are often composed of aragonite. This takes place in caves where groundwater has dissolved limestone rocks to form caves and deposited minerals through evaporation.
These crystals can also form on cave walls from seeping water or from dripping mineral-rich waters that build up over time, creating flowstone formations.
Rockcloud Natural Aragonite Calcite Cluster
Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (CaCO3), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation from marine and freshwater environments.
These are deep orangish brown clusters that are just abundantly studded with small to large rods on all sides. Aragonite makes a beautiful and a great display size.
Magnesite
Magnesite is found in limestone caves, naturally rich in carbonate minerals. Its chemical name is magnesium carbonate, with a chemical formula of MgCO3.
This white powdery mineral helped to make cement for centuries—and even today, it’s still an essential part of concrete production. It also plays the role of a catalyst and filler in the production of synthetic rubber.
Anthodites
Anthodites are a type of mineral formed from the decay of other minerals in caves. They’re found in caves, where they have the opportunity to absorb moisture from the cave walls.
They can be used as gemstones in jewelry, but this is rare. It’s challenging to find enough anthodites to make any reasonably sized piece.
Sulfides
Sulfides, also called sulfide minerals, occur in many colors; some are more beautiful than others. The most common colors are black, brown, or yellow.
Sometimes you will see sulfides that are bright red or orange; these colors are usually from iron compounds in the mineral (recall our discussion of rust).
As we discussed previously, sulfides form from hot springs and volcanoes. They are often found near hot springs because this is where hydrothermal fluids flow through rock and create conditions for their formation.
Borates
Borates are the salts of boric acid, which is found in many caves. Since boric acid does not dissolve in water, it can be isolated and used as a preservative for fruits, vegetables, and meat products.
It is also used to make glass or ceramics. Borax has been used as a flame retardant for years and was even used by the ancient Romans to keep their armor from melting during battle. This mineral is an essential part of our everyday lives. Boron is present everywhere in our environment, but finding large deposits of concentrated borates is rare.
In the image on the left, we see one of the main sources of borates.
Arsenates
Arsenates are a group of minerals that contain arsenic and oxygen, and they often associate with other sulfates, such as gypsum, calcite, and anhydrite. These crystals are extremely rare and not widely used commercially or industrially.
The following arsenates were found in the active sulfuric acid caves of Aghia Paraskevi: arseniosiderite, beudantite, conichalcite, hörnesite, manganderzelitite, mimetite, olivenite, pharmacolite, strashimirite and talmessite.
Carbonates
Carbonates are minerals that contain the carbonate ion CO32-. They are ubiquitous in caves and other subterranean environments because they form due to chemical reactions between groundwater and limestone rocks. Carbonates include calcite (CaCO3), aragonite (CaCO3), dolomite (MgCO3, CaCO3) and siderite (FeCO3).\
Nitrates
Nitrates are a group of salts that contain the nitrate ion. They are formed by the action of bacteria on nitrogen-containing compounds, such as proteins and amino acids.
You can find nitrates in caves as nitrate salts. Essentially concentrated, non-poisonous forms of fertilizer, we advise you not to taste them.
In addition to fertilizers, some forms, like ammonium nitrate, can contribute to explosives. Nitrates have many uses in medicine as well.
They’re used to treat certain cancers like leukemia, help clear up pneumonia symptoms faster, relieve pain after surgery or injury, prevent low blood pressure during surgery or labor pains (epidural), and relax muscles when injected into them before an operation (neuromuscular blocking agents), control heart rhythm disturbances such as atrial fibrillation.
Silicates
Silicates are a group of minerals formed by an acid’s reaction with a base. They are made of silicon, oxygen, and other elements such as aluminum, iron, and manganese.
Silicates can be found in caves, but not all contain silicate formations such as stalactites or stalagmites.
Vanadates
Vanadium is a chemical element with the symbol V and atomic number 23. It is a complex, silvery-gray, ductile, malleable transition metal. The element is naturally found in various minerals and fossil fuels like lignite.
Vanadium was discovered by Andrés Manuel del Río and Pierre Louis Guédot in 1801 at the mines of New Spain (modern-day Mexico). Vanadium occurs primarily as vanadium pentoxide, V2O5.
Phosphates
Phosphates are essential for plants and animals. Found in the soil, rocks, and water, phosphates are used in fertilizers and detergents. They also make up part of the structure of bones, teeth, cartilage, and DNA molecules.
Phosphate mining is a big industry worldwide because it is so helpful to people in many ways. The phosphate minerals mined from mines or quarries allow production many of our beloved plastic products (like toothbrushes or bottles using polyethylene terephthalate).
Conclusion
Caves are a fascinating place for scientists to study their minerals. The unique environment provided by caves makes them ideal for finding new minerals that can be utilized in various ways, often improving our everyday lives.
When you go on your next trip, pay close attention to the minerals along the walls. See if you can spot any of the ones on this list. Chances are, you’ve already seen several of the more common ones, but what about the rarer ones? Leave a comment if you find something special!