Rare Antiquities & Ancient Artifacts

Earth’s rarest minerals

By Jonathan Amos

BBC Science Correspondent, Washington DC

Fingerite from El Salvador is “a perfect storm of rarity”

Scientists have categorised the Earth’s rarest minerals.

None of 2,500 species described is known from more than five locations, and for a few of them the total global supply could fit in a thimble.

The researchers say it is important to hunt down these oddities because they contain fundamental information about the construction of our planet.

Some will also undoubtedly have properties that are useful in technological applications.

The list appears in a paper published in the journal American Mineralogist. It is authored by Dr Robert Hazen, from the Carnegie Institution in Washington DC, and Prof Jesse Ausubel of The Rockefeller University, in New York.

“Scientists have so far tracked down 5,000 mineral species and it turns out that fewer than a 100 constitute almost all of Earth’s crust. The rest of them are rare, but the rarest of the rare – that’s about 2,500 minerals – are only found at five places on Earth or fewer,” Dr Hazen told BBC News.

“And you ask: why study them; they seem so insignificant? But they are the key to the diversity of the Earth’s near-surface environments.

“It’s the rare minerals that tell us so much about how Earth differs from the Moon, from Mars, from Mercury, where the same common minerals exist, but it’s the rare minerals that make Earth special.”

Image copyright R.DOWNS/UOFNEVADA

The entire world’s supply of cobaltarthurite would probably fit into a thimble

Minerals are combinations of chemical elements arranged into crystalline structures. Earth’s rocks are built from different aggregations. Think of feldspar, quartz and mica – these are the ubiquitous species that everyone knows.

But cobaltominite, abelsonite, fingerite, edoylerite – these are examples that will not form unless the “cooking conditions” are absolutely perfect.

The atomic ingredients must sum exactly, the temperature must be precise to the degree, and the pressure will have to be defined in the narrowest of margins.

And then, some will immediately fall apart when they get wet or the sun shines on them.

Edoylerite, metasideronatrite, and sideronatrite are examples of vampire-like minerals that decompose on exposure to light.

Nevadaite is only known from just two locations: Eureka County, Nevada, and a copper mine in Kyrgyzstan

Hazen and Ausubel have put their list of 2,500 species into four broad categories of rarity that speak to the conditions under which they form, how rare their ingredients are, how ephemeral they are, and the limitations on their sampling.

“Fingerite is like a ‘perfect storm of rarity’,” said Dr Hazen.

“It occurs only on the flanks of the Izalco Volcano in El Salvador – an incredibly dangerous place with super-hot fumeroles.

“It’s made of rare elements – vanadium and copper have to exist together, and it forms under an extremely narrow range of conditions. If you just change the ratio of copper to vanadium slightly, you get a different mineral. And every time it rains, fingerite washes away.”

The new catalogue allows scientists to begin to gauge just how large the reserves of a particular mineral ought to be, and where those reserves might be. And for the technologically useful ones, this will have enormous value (although it is often possible to synthesise these minerals industrially).

But the exercise also provides important insights on Earth itself. Many of these minerals would be absent altogether if not for the presence of biology, which moderates the chemical environment in which minerals forms.

In that context, the paper contributes to the Deep Carbon Observatory project, an international venture that seeks to understand carbon’s role in the Earth system.

It is thought there are just over 100 carbon-bearing minerals out there waiting to be found.

Hazenite: Microbial “poop”

Dr Hazen actually has an entry named after him in the catalogue.

Hazenite is only known from Mono Lake, California. It forms when the phosphorus levels in the lake get too high, and the microbes in the water, in order to survive, have to start excreting it from their cells.

The resulting tiny, colourless crystals are essentially microbial “poop”.

“Yes, it’s true – hazenite happens,” said Dr Hazen.

Ichnusaite: Contains the radioactive element thorium and lead-like molybdenum, with only one specimen ever found, in Sardinia

The Grape Agate gemstone is a relatively new find, 2017, from Indonesia. Although the common name is Grape Agate, these are really Botryoidal Purple Chalcedony. Botryoidal means that round tiny sphere-shaped crystals that have naturally formed together. 

Chalcedony is not scientifically its own mineral species, but rather a form of Quartz in microcrystalline form. It is a form of silica, composed of very fine intergrowths of quartz and moganite.

Chalcedony appears in numerous ways. It sometimes occurs in geodes, lining the cavity with small round blobs. Its agate variety is also found in geodes, commonly lining the outer layer underneath the larger quartz crystals. Chalcedony also forms pseudomorphs after organic material.

A well-known, and most common example is petrified wood, in which the wood has been completely transformed into various colors of chalcedony. In the Petrified Forest National Monument in Arizona, an entire forest was transformed into petrified wood. What is left of the forest can be seen in the myriad of agatized trees.

For most of time, chalcedony was thought to be a ‘fibrous’ variety of cryptocrystalline quartz, but more recently, it was actually discovered to be a combination of quartz and another silicate mineral; moganite (a polymorph of quartz). Both quartz and moganite share the same silicon dioxide (SiO₂) chemical composition, but they have varying crystal structures. Moganite is monoclinic, while traditional quartz belongs to the trigonal crystal system. Chalcedony forms with a hexagonal crystal structure. 

As the defining mineral for 7 on the Mohs scale, it is a rather hard mineral and is good for jewelry. The actual name ‘chalcedony’ originated from the latin word ‘Chalcedonius’, which is thought to be derived from ‘Chalcedon’, an ancient seaport of Asia Minor, now Kadikoy, Turkey. 

A common form of chalcedony is compact silica most often found in sedimentary and volcanic environments. Formation occurs over a long period of time, as minerals are slowly deposited into a pocket of another type of rock, such as granite. The most abundant chalcedonic deposits are in areas that host volcanic rock . In many cases, silicon dioxide forms in sometimes readily visible and parallel bands, as seen in banded agate.

Many semi-precious gemstones are in fact forms of chalcedony, although in the gem trade, the name chalcedony usually describes only white or blue chalcedony. 

The more notable varieties of chalcedony are: Agate, Iris Agate, Binghamite, Bloodstone, Carnelian, Chrome-Chalcedony, Chrysocolla Chalcedony, Chrysoprase, Jasper, Dallasite, Orbicular Jasper, Onyx, Sardonyx, Petrified Wood, and Pietersite. Petrified wood is one of the most common forms of chalcedony.

Metaphysical Properties

Grape Agate is a tranquil and gentle stone. It promotes inner stability, composure, and maturity. It’s warm, protective properties encourage security and self-confidence. It allows for deep and intense levels of meditation in a short period of time. Grape Agate is a crystal of dreams, intuition, and luxury. It is a healing crystal of the crown chakra.

Purple Chalcedony acts as a psychic stimulator and protector, as well as a caller of visions and dreams. Both Purple and Blue Chalcedony activate the third eye chakras, but Purple Chalcedony’s frequency accesses the deepest levels of the subconscious, bringing long-hidden blockages, memories, or patterns into consciousness. It is a powerful stone for journeying consciously through the dream state.